Pointless zone thermostat

Diz

I have a two zone home. One zones smart thermostat is in a ground floor hall way which works ok. The second zones smart thermostat is in the main bedroom with a free flow radiator. I want to put a smart TRV on the radiator and just use the wired smart thermostat to drive the zone switching. Do I need an open flow radiator (guess the main bathroom would do)? Can you have two make the wires smart thermostat essentially a remote switching point for the smart TRV’s in the zone?
Thanks