To not tighten back muscles during sleep: (1) throw away the bed; (2) turn up the temperature in the bedrom; (3) sleep on the floor; (4) get a new firm bed; (5) do not sleep on any sofas; (6) take a hot water shower for twenty minutes or more before going to bed.
Alternate ways to increase the temperature in the bedroom: Use an air dehumidifier (the opposite of an air humidifier). The air dehumidifier will take out the moisture in the air and heat up the room. On automatic mode, it’s “loud motor” will be turning on and off throughout the night, and this will disturb most people’s sleep.
Another alternative way to increase the temperature in the bedroom is to sound-proof the room with the filling material we generally install under the ceiling.
A third way to increase the temperature in the bedroom is to buy several cheap carpets and cover the entire bedroom floor with several layers of heavy carpets.