I have two 12X14 "Colorado" Wall tents I bought used. I wouldn't go any smaller than the 12X14 for what you described. I have a wood stove that I modified to utilize a wood pellet burner. The wood pellet feeder allows you to fill the hopper right when you go to bed and set the burn rate, and not have to refill until morning. When spending time in the cold, I hang small tarps on the horizontal supports and cover the roof with a larger tarp. If you have a tarp covering the roof, you'll need a long rope to lace across the roof tarp (serpentine patter) in the event of some wind. Tie the rope to the stakes anchoring the tent. The combination of hanging tarps inside and over the roof, helps hold the heat. I, also, place a plastic tarp on the floor as a moisture barrier and then cover this with a few rugs. I may look like a gipsie, but camp is comfortable.