Really not interested in paying a subscription. Trying to get away from all that.The easy way is to get a Nabu Casa subscription. That way you can expose your HA lights, switches, etc to Alexa and just go from there. It's a straightforward and generally frustration free way to do it.
What make are your TRVs? I have a Hive set up and the main obstacle for me was ensuring the boiler turned on when the TRVs were turned on