[Izkata]

HomeAssistant supports a bunch of home automation systems, including local-only ones like ZWave and Zigbee*. A search for "zwave thermostat" comes up with a lot of results, though I couldn't say how difficult it might be to configure them (I'm only using simpler devices like switches and sensors).

* There are internet-connected controllers and local controllers so you'd also want a local controller. I've used an Aeotec Z-Stick for ZWave devices for around a decade, it plugs into USB, HomeAssistant accesses it directly, and the ZWave network itself is connections between the Z-Stick and the devices without the internet.

[floating-io]

The Honeywell Z-Wave thermostats are trivial to connect and work with via Home Assistant.

Source: I own one. :)

[acidburnNSA]

I own two and they are bulletproof with Home Assistant. When away from home I just wireguard in and adjust/monitor as needed.