We installed a Hunter Digital Thermostat Model 42999B ($19.95 at Wal-Mart) two years ago and have been very pleased with the result.
https://get.google.com/albumarchive/...wVt8An2do-f5bm
This model operates on a 14 volt
or millivolt system (millivolt system requires two AA batteries to activate). It has the ability to run a fan and an air conditioner . . . but we only tied in the heating leg. No more 5 to 10 degree temperature swings. You do need to remember to turn the thermostat heat switch to the
off position before closing down.