Giant in the Playground's Increasing Size, Effective Size, Unarmed Damage, Reach thread is of some limited utility.
Minmaxboard's Grappling Handbook, Hulkamania is runnin' wild, is of somewhat more use.
From your current position, I suggest the following.
Option 1: Sorcerer
No, really. Enlarge Person as a spell gives you +5 to your grapple modifier. It comes in a cheap wand at your level. Babau Slime increases your grapple damage with a bunch of acid (scales with caster level, buy a higher CL wand). Fearsome Grapple is a level 2 spell, so 4500gp, i.e. 'you can afford it', and adds +4 to your grapple mod. Another level 2 is Balor Nimbus, 6d6 to anyone grappling you per round. Corrosive Grasp creates multiple touch attacks, so you do normal grapple damage and it sets off the touch attack for +1d8 acid each time. Fist of Stone gives +6 enh to strength and a natural slam attack, but only for a minute. Of course, timing all this short-duration buffing requires an ambush on your part, so why not buy a wand of Chameleon to help hide, or Invisibility for sneaking around.
You'll also have an Octopus familiar from Stormwrack, for another +3 to grappling.
Sorcerer avoids having to make use magic device checks to use the wands - if you have a friendly arcane caster willing to sneak along with you and buff you for your grappling ambush, then you can forgo this option entirely.
Option 2: Warblade
Non Tome of Battle classes count as half initiator level for determining eligibility for maneuvers. So a level in Warblade with your 11 other levels counts as a 6th level Warblade, meaning you can select 3rd level maneuvers. A 3rd level maneuver (it's a stance) is Crushing Weight of the Mountain. It gives you the Constrict ability. Other than a Soulmeld, this is one of very few ways to get Constrict in the game without changing shape. Constrict is amazing, because ANY TIME YOU ROLL A GRAPPLE CHECK, even to /enter/ a grapple, to do unarmed damage, when they try to escape, WHATEVER, you get to do Constrict damage. Yes, in addition to your unarmed strike, yes, in addition to entering the grapple damage, yes every time they try to escape. You just squeeze the life right out of them. Crusader provides a better chassis, and also has Crushing Weight of the Mountain, but warblade has access to Iron Heart Surge which is very barbarian.
Option 3: Totemist
At level 2 in Totemist from Magic of Incarnum, you grow an extra pair of arms and add your essentia x 2 + 4 to your grapple mod. At this level, with the Expanded Soulmeld Capacity (Totem) feat, that's +12 to grapple. Also grants extra natural attacks from the arm, and other stuff from other soulmelds (short-range teleport, Spell Resistance, Natural Armour, Fire Resistance, etc).
Doesn't really do much for you this level, though. A good choice to take after you've dipped the low-hanging fruits in Warblade and/or Sorcerer.
Feat: Scorpion's Grasp
From Sandstorm, this feat lets you basically have improved grab for unarmed strikes and one-handed weapon attacks. It lets you punch someone, grab them, succeed on a grapple attempt, punch them again, and still have the rest of your actions free to punch people. The best part of Improved Grab, however, which is grappling at a -20 to count as not grappled and building a big ball of weak enemies that you carry around with you and use as a melee weapon, is sadly absent.
Feat: Snatch
Requires claws or bite, MMII. Gives Improved Grab, and the ability to fling creatures 3 sizes smaller than you far, far away. Totally awesome.
Feat: Open Lesser Chakra (Arms)
Combined with a level in Totemist to get access to Kraken Mantle, binding the Mantle to your newly opened Arms slot will give you +2 to grapple per Essentia placed in (max 3, for +6 to grapple untyped).
Item: Gloves of Titan's Grip
From MiC, 3/day activate to get +8 Enhancement to Grapple for 7 rounds. Strength boosts are usually enhancement, but nothing really enhancements grapple except Grip of Iron, so this is great. Totally great. Buy it.
Item: Scorpion Claws
From Sandstorm. Exotic weapon that grants +4 to grapple checks. Well worth it, possibly even if you're not proficient.
Notes
Scaled Horror prestige class from Savage Species requires the 'Aquatic' or 'Reptilian' subtypes. You could make an argument that as a Dragon Disciple, you're kind of doing that. If so, it picks up Improved Grab at first level. Warblade -> Scaled Horror would be a great power boost.
Black Blood Cultist from Champions of Ruin is normally great for grapplers, but you're too high level and it overlaps with Dragon Disciple, also your alignment is wrong. Avoid it entirely.
Psychic Warrior is a great class for grapplers, but at this level you get too little benefit and too few power points to be of any use. The two key powers are Grip of Iron and Expansion, but they both want Augmentation to be great. There are more Wizard/Sorc spells that benefit grappling than there are powers, so even if you grabbed some Dorjes, it wouldn't be as worth it as a Sorc dip. Check the second link for more spells/powers that help out grappling.
Aberration Blood - This feat sets you up for Inhuman Reach, a natural reach increaser. It also adds +2 to grapples. At this level, it's probably sub-par.
I'd recommend more of a Two-handed weapon Fighter or Barbarian in lieu of using Two-Weapon Fighting.
There are multiple reasons to do so, such as the Accuracy penalties you get from Two-weapon fighting lowering your overall damage, being unable to utilize Power attack fully because of said accuracy penalty, and the fact that your gold is being spent on two weapons instead of just using all of your gold on a single weapon.
Also, Barbarian gets a D12 hit die against a Fighters D10, gets a full Base attack bonus progression, and their rage ability gives them bonuses to blanket will saves instead of just will saves against fear like the fighter, Along with a Substantial bonus to Strength and constitution when raging. ( Not to mention you probably aren't going to use all your rages in a day later in your game )
As far as your stats are concerned, for your TWF Fighter, You have the right of it. Strength, Dex, and Con are your most important stats, wisdom being secondary for will saves. Strength will contribute to your damage, Dex will boost your armor class, Con will increase your HP quite a bit.
You'll obviously want the Two-Weapon Fighting feat, So that's one of your feats. For your other two You're level four, so you could take Improved Initiative to improve your chances of getting the first action with your dexterity, and Jaguar Pounce so that if you do get the first action you have a pretty good chance of getting the jump on someone and using the high crit ranges on your light weapons to get a crit off when the fight starts.
I believe using a non-light weapon in your main hand, and a light weapon like a dagger or shortsword in your off-hand is still considered standard with TWF, But since you'd be using two weapons you'd want your weapons to threaten more, so a mainhand Scimitar to vary up the types of damage you deal ( Slashing v. Piercing ) while giving you a larger crit range on your main hand would be the best.
So I've got based on the stats specified: Str: 18, Dex: 16, Con:21, Wiz: 12, Int:10, Cha:10
Feats: Two-Weapon Fighting, Double Slice, Two-Weapon defense, Weapon Focus: Scimitar, Weapon Specialization: Scimitar, Jaguar Pounce, Improved Initiative
That puts you with 4d10+20+4HP, With a 1d6+6 Main hand. If your opponent is flat-footed your crit range is 15-20/x2, When they aren't its 18-20/x2. Your offhand is 1d6+4.
This should deal enough damage in the first round to get an enemy to focus on you instead of on someone else in your party should you roll a crit. Later on when you hit level eight you can retrain your Jaugar Pounce Feat into Improved Critical.
Some other feats you may want to look into as you level are Furious Focus, Shield of Swings, and Pushing Assault, These work well with Critical builds as if you push a target more than 5ft away, they cant use a full-attack action during that round if they don't have pounce.
Best Answer
Be an Incarnate or Totemist
Looking at the incarnum handbook, your stats line up perfectly with their priorities, it can synergize well with a dip into swordsage (lucky you), and is an interesting and flavourful route.
The only trick is that the book doesn't explain itself well, so an amount of research reading the explanations in the handbooks (incarnate handbook + incarnum handbook + swordsage handbook + Totemist Handbook) is clearly indicated. Beyond that, it fits your requirements perfectly.
Beyond that, the fluff of an animated construct armouring itself in soulstuff just begs for plot, which is, itself, interesting. Your first level of swordsage is an interesting dip, as it provides skills, stances, and attacks that can provide some absolutely fascinating synergy with your invested soulmelds. You'll have to spend time working through the combinations, but it'll provide character-career long flavour and moves that will direct how you spend your essentia.
Unfortunately, you will want to plot out your character's build out to the conceivable end of the campaign. You're integrating two of the later and extremely fiddly systems (for the perfect trifecta, dip into binder just to watch your own head explode.) But, with enough research and preparation, this fits your requirements nicely, and provides a serviceable tier-3 character dripping with interesting questions.
In terms of integration, you'll actually want to advance swordsage more than you might expect. The Diamond Mind school that the swordsage has access to is concentration/constitution driven. The incarnate has concentration as a class skill, and by taking advantage of the clause that notes that half of other class levels go into your initiator level, there are some cute tricks. Specifically, you want swordsage 2 after you take 4 levels of incarnate/totemist, giving you access to third level maneuvers, all of which can be diamond mind, allowing you to apply concentration to many of your saves and damage rolls.
Ask your DM if you can retrain to have the following maneuvers:
Choose your stance based on your intended incarnate build and this guide. Your other 2 maneuvers should be a function of your intended build as well, chosen with an eye towards meeting prereqs.
Dipping back into swordsage at level 6 allows you to cherrypick other diamond mind maneuvers and stances, which will neatly complement your incarnate. While it's likely going pure incarnate is better, there's no reason to not mix it up once you've fallen down this path.