I also just got AC last year, and while it doesn't have as many fancy features I'm glad I got one that works with standard 24V HVAC wiring. I built my own thermostat out of an ESP8266, I²C temperature sensor from adafruit, and three TRIAC circuits to control the fan, heat, and ac wires. Connected to MQTT and I can send control commands to it from my Home Assistant instance!
If you have the code for this publicly (or would consider making it so) I would be quite interested in it.
There are a fair number of DIY thermostat projects online, but all that I have found were one-offs by their creators, or were for specific kinds of systems like boilers.
I've been batting around the idea of starting a general-purpose IoT thermostat that only uses cheap, widely-available components that anyone can easily duplicate with a BOM and 3D printer.
My first model is pretty janky and definitely built as a one-off, lots of hard-coded stuff in the arduino code I wrote for it that are specific to my setup. I've been thinking about making a new, more streamlined version that could be fully assembled by a fab and sent ready to flash and wire up into an HVAC system. And of course, I'll publicly release the KiCAD files and code for that when it's ready! :)
