I have a cheap, old Williams wall furnace that is controlled with a 2-wire millivolt thermostat. It doesn’t look like any of the normal IoT vendors make a smart thermostat for it. I’ve seen some people get success by hooking up a 24V thermostat with an external power supply, but I’d rather not go down that route if at all possible, both for aesthetics and jankiness reasons. I could hook up a relay with a fully-custom controller, but then I’d have to worry about the temperature control logic, power management, and the possibility of freezing my pipes if anything I do breaks.

Is there anything made by a reputable vendor that I can connect to HA?