I use esphome & a 4 channel relay to engage the HVAC stages. I built a virtual thermostat in home assistant and tied it to a Shelly e-paper temperature sensor. I can move it to other sensors in the home if/when needed or carry the sensor around the house. It's not a huge place though.
I have the old school thermostat still on the original mount point in case of catastrophic failure and for aesthetic.