Small tent only needs small heat. I used to use a tarp lean-to with a hatful of fire and the toboggan and log stack rigged to bounce heat back at the tarp. Really good sleeping bag. If I got cold enough to wake up I could reach out and slid a few pieces of wood into the fire to build it up a bit, little warmth and back to sleep. One time I did wake up to find my husky mix had managed to slide inside my mummy bag, he was warmer, I was warmer, it worked.
Got older went to a 3-4 man tent for two people with a candle lantern or small propane lantern on low for heat. Could keep the walls from being frozen for about 2 feet off the ground. So over 32* where we were sleeping.
Cold isn't a problem if you can stay dry. Rain and cold is a disaster. One I have hit a few times in the rocky mountains so I'm guessing the mountain men had it to deal with on a regular basis. Even with modern gear it is unpleasant. Tolerable but not pleasant, even less so if one isn't able to just hunker down and wait for weather to clear but has to pack and hike. Even packing a car and unpacking to set up are dismal with wet conditions and chilly temps. Imagine a pack horse isn't better.