OK, take a look at the simple thermostat, Simple thermostat with preset modes management . It’s a derivate of the generic thermostat. It supports true preset mode management. As long as you use a preset mode, it preserves settings at restart. But it does not work well with preset ‘none’. Then you must a target value in the config that kícks in at restart.
Hm, I have Sonoff switch as well, 01MINIZB,…