I agree with Gary that losing that protective layer of fat is big factor in being cold. My wife is also very slender at 104 lbs and 5'4" and like Gary, I never really understood just how cold she found "regular" air conditioning until I had to wear a full winter coat inside AC chilled places. I had never really been cold before the Cancer even though I was slender also.
But it became abundantly clear that weight loss just did not account for how cold and weak I continued to feel until I started on the thyroid pill. I don't weigh even one pound more than when I finally got thyroid medication yet I am now warmer than my wife. If my doctors had not all been so quick to blame weight loss for being cold, I could have started being warm and energetic much earlier.
I think there is a synergistic relationship between weight loss and thyroid damage that amplifies the negative effects of each. Like in Math quizzes, both factors of the equation need to be balanced to solve this problem
Charm