Replace all-or-nothing homeostasis toggle with a logistic function.

To test, put yourself in a situation where you're wearing a lot of high warmth clothing, but comfortable.
before the change, once your body temperature stabilizes (saving and loading seems to force this to happen?), the per-bodypart comfort level in the armor layering menu will toggle wildly back and forth as reported in #9671.
Afterwards it should shift up or down by a single point per turn at the most, more likely it's going to shift much less often.