Our ancestors had a good idea borne out of need, bed curtains. In unheated houses or wood burning only, heat was at a premium. Coupled with a canapy of some kind and they make an indoor tent. Why you ask do you need an indoor tent? If you live in a cold climate in winter, you may loose electricity, for an extended period perhaps. Sometimes especially if you live in a relatively remote area it can be longer, or more often. An indoor tent gives you place to go be relatively warm, especially when sleeping.

I have a poster bed so this was easy. I made a removable framework that attaches to the posters a bit higher than sitting height, no need to make it much larger. Wool blankets (I buy them whenever I see them cheap, even used ones, They have dozens of uses including car carry, capotes, ponchos, bed blankets, hats, mittens, clothing) make up the canapy and bed curtains. If you like a bit of fresh air you can leave gaps on edges. Body heat and your breath will help keep this warm when occupied.