If you had ever been in an unheated building, you’d know that warming up from your own body heat alone is impossible — even in the tightest enclosed space. Trust me, I know what I’m talking about.
And if you’re already frozen like in the game, or worse — wet — you’re done for. You’ll just die from hypothermia unless you find a heat source like a campfire.
I also really dislike that there’s no way to control the temperature that affects crops, other than using greenhouses, which only give +5 degrees. In real life, you can create shade, cover the crops with tarps like they do on farms, or simply water them generously to cool them down — and again, sadly, none of this is possible in Vintage Story.