I have my thermostat set to 50f (10c)... only because any colder and I worry about pipes freezing. I'm on the computer all day, so I sit in a sleeping bag and have an electric hotpad on my hands. It works fine for me, I can still get in "the (programming) zone", even while I'm on day 4 for a water only fast, which typically drops my metabolism and therefore my perception of body temperature. (I'm a pretty extreme person...) I typically do this every winter, but especially this one because fuck the war.