Which weapons are considered “upgrades” in TF2

If you don't mind playing as a sniper, Sniper Paintball RC1 scales down well.

However, why not just enable bots?

Here is an instruction on how to create a server and put bots on it:

1. Make sure you have the port 27015 accessible for connections.
   ^{How? Look here.}
2. Open the game console.
   ^{How? Options⇨Keyboard⇨Advanced...⇨Enable developer console. Press ~ / ` to open the console at any time.}
3. Type sv_lan 0 if you want the game to be public, or sv_lan 1 for LAN only.
   ^{Public server is recommended}
4. Type map <mapname>, replacing <mapname> with the name of the map you want to play.
   ^{Or press the [+] to the right of BROWSE SERVERS in main menu instead.}
5. If the server is public and you don't want anyone to intrude, you can set a password:
   Type sv_password <pass>, replacing <pass> with some simple password.
   _{(e.g. sv_password 1234)}
6. Set the bot difficulty: tf_bot_difficulty <x>, where <x> is from 0 (the easiest) to 3.
   ^{(e.g. tf_bot_difficulty 0)}
7. Add bots: tf_bot_add <team> <class>
   <team>: red | blue
   <class>: scout | soldier | pyro | demoman | heavyweapons | engineer | medic | sniper | spy
   ^{(e.g. tf_bot_add blue heavyweapons)}
   To remove all bots: tf_bot_kick all

Here are some ways for your friend to connect. If one fails, try the next one.

• Join the game via Steam.
  ^{In Steam Friends list press ▼ and Join Game.}
• In console: connect <ip>:27015, where <ip> is your (server's) IP address.
  ^{(e.g. connect 11.22.33.44:27015)}
• Try the same thing with your (server's) local IP address (find it in Windows/Linux)

If nothing works, see the step 1 of server creation instruction.