FWIW, to save propane, I lower the thermostat down to 50 at night, just enough to keep the pipes and things from freezing.
I bought an electric mattress pad heated cover to stay warm, (one of the best things I ever bought I think) and then in the morning, fire up the furnace and electric heat to take the chill off.
If it's going to be a cold day, I just leave the electric heat on (not unattended), dress warmly, and use the propane only when necessary for heat.
I usually make it about 3 weeks before I need a refill (30# tank), and until I refill, I just switch to the other tank.