There was some research done a while ago that showed that if you keep your head warm, the rest of your body doesn't notice the cold as much. A tv show over did an experiment where they put two guys wearing just their boxers into a cold store and timed how long they could stay there. The guy with the hat lasted a lot longer than the bare headed guy. So when temperatures drop indoors, wear a hat and a smile.
There's a saying.. nudists might be a bit crazy but we're not stupid! If I'm cold I'm going to put something on. Usually a t-shirt will do it. We have two wood pellet stoves to heat our house so we are able to keep temps in the 'able to go nude range' without going broke. And if we're hosting a nude party I'll crank up the heat even higher so everyone is comfortable nude. And there's always the hot tub outside at 102f.
We built our home about 10 years ago. I used in floor heat as my heating design. My design by the way we can keep the house 75 plus no matter how cold it gets. Lots of extra insulation in the ceiling and floors. If your feet are warm you are warm. Nude 24/7 year round in Northeast PA. The only reason we still live here.
Greetings from close to Arctic Circle (our home is on 62nd Latitude)! It is very individual what one perceives as comfortable temperature to be nude. Whereas in warm season outdoors +17-18 C is enough to enjoy outdoors nude, indoors the temperature is somewhat a question of preference. In our family we have established that +23 C is enough, with +22 C and lower socks needed and maybe a t-shirt, too. Otherwise, personally I wouldn't go over to textile life in my own home. Simply too complicated. Being nude indoors also produces much less laundry. Down side being higher energy costs especially if house insulated badly. Our house is well insulated, so even if outdoors -40 C, indoors comfy +23-24C.
At our resort...and home...we wear fairly heavy fleece house coats when it's really cold. Still get nude time indoors, in the hot tub, sitting by the camp fire, etc. In the words of a very experienced nudist friend, "hey, we're nudists...we're not stupid!"