I have a HASS 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 HASS.
Unsure more details about your under-floor system, but assuming it’s anything close to using a ‘regular’ thermostat, hopefully the above link to a # of similar threads helps.
Under Floor or radiant floor heating is still somewhat of a niche area for thermostat’s. One that I use and recommend is the NuHeat Signature. It’s Wifi, uses a cloud API but has a component for HASS. It’s also expensive.
Floor heating is specifically different as the thermostat needs to have a floor probe to prevent overheating the flooring material and warping/damaging it.