Read a long time ago about a European that thought Americans over-heated their houses. Since I liked the erasure-of-boundaries from inside and outside that came from leaving windows open always ... my kids grew up with the windows open, almost always, for more than a decade. Admittedly, this is an easier thing in southern California than elsewhere.
Found that a skinny pre-teen daughter could be warm wearing shorts when the indoor temperature was in the 60's. (Check ears, cheeks, forearms for chill - and always OK.)
Not so sure about much lower temperatures, simply as that is outside my immediate experience.