I recently emailed stelpro who makes zigbee and zwave baseboard heat t-stats and got this response.
We are planning to release a floor heating thermostat compatible with our Maestro smart home system in 2019. However, I have no release date available.
So here is to hoping for a $100ish zigbee floor heat controller!
There's also sinope Zigbee thermostat for basboard and infloor heating. I have 12 of the baseboard thermostats and one infloor thermostat. Unfortunately they were bought before the Zigbee version release. I have the wifi neviweb version.