What I do when its winter is make a very very small "fort" of blankets, like one would do as a child. Since I have electricity my PC running makes it more than warm enough. Also I bought a 350$ sleeping bag thats like -30 or some shit. If push comes to shove I will make pic related. Also from walmart you can get foam camping pads, on just a wood floor I place two then the sleeping bag
Even with just the layers of blankets around you normal body temp will make the fort warm