Wiring – How To Run Thermostat Cable Without Going Crazy

I've read a hundred questions on this, and most of the answers come down to solutions I've tried that don't work, hiring an electrician, or doing some very messy work. I'm hoping there's some way to simplify things.

Here's what I'm dealing with:

• A 3-zone heating system: Basement, Ground Floor, and Second Floor. Gas boiler is in the basement. Zones each have their own thermostat. Baseboard hydronic heating.
• 2 wires controlling each t-stat. No C Wire. 🙁
• Ground Floor has an older Nest, with enough battery backup it hasn't run into issues
• Basement and Second Floor have basic cheap t-stats
• I bought two Ecobee 3s before I understood all of this, months ago. Now, after months of learning, I'm not seeing an easy solution, just a bunch of messy ones.
• I can buy Nest 2020 t-stats, but they're unreliable without a C Wire, and have lousy battery backups. I want to get a C Wire, do this right. I'm not leaving this house until I die.
• Basement wiring is loose. I can pull the cable right through and hook up a 3 or 5 wire setup, easy. I've found where the C wire would connect to. All good.

The Second Floor is where all the problems are happening. The cable is not loose. Based on what I've read, it's likely stapled to the studs or to something somewhere. 🙁 Fishing isn't an option here. Every answer I've read says I'm not going to be able to successfully pull those staples out.

I don't have ductwork I could run it through. The ducts come from the attic and go everywhere except the basement 🙁

The basement has a finished ceiling, not a drop ceiling. 🙁 The attic is mostly finished, and I don't see any wiring up there that would provide a guide on how to get down 3 floors, but I'm exploring.

So, what haven't I thought of? I could rip off the baseboards, make a clean hole to get from Floor 2 to Floor 1, but that won't get the wire across the basement ceiling. I could pull up the hardwood floor on Floor 1 to get across, but that sounds messy. I could try running cable up to the attic and look for a straight shot down from there, but I doubt it exists. I could borrow/rent a thermal camera, look for where things are running in the walls, and try to find the cleanest route to run things before I start making holes, and, if I'm lucky, find a simple shot.

Anything I'm not considering? I see a relay that lets you connect a 5-wire t-stat to a 2 wire boiler by sitting in between and handling the messy stuff, but, of course, that's not what I need. If there were a relay that could stand between the t-stat and the boiler, sending power on one line and signal on another, and then send the proper two wires from itself, that would be great, but I'm not seeing such a product.

This is driving me nuts. I'm really trying to avoid driving the wife nuts by breaking up walls and/or floors everywhere, or spending hundreds just to run a wire, but I'm not seeing a third option.