You can use the generic thermostat of Home Assistant, if you are OK with only using a software thermostat. All you need in that case is a temperature sensor and something to switch the floor heater valve. There are plenty options to make something like that. If you want something reliable you might consider the ControlBox (I developed that electronics for our own house, we are in pre-launch state at crowdsupply with it).
For better control of the temperature you might also want to have a PID thermostat.