I have a openHab installation with only zwave devices (about 30).
I have a thermostat that control underfloor heating system.
Now I plan to change this old thermostat with one that I can control with openHab.
I’m creating a Smart Virtual Thermostat (beta version). You only need a temperature sensor and a actuator for switch the boiler/heater on/off.
Maybe that is something for you.
Otherwise, a hardware zwave thermostat is available from Secure. I thought the srt-321