Enter the very long flannel nightgown I either bought or was given longer ago than I can remember. Late 80s, I think; maybe earliest 90s. Never wore because I used to be warmer in my youth. (That or kept the heat on all the time; I fancy it was the latter.) Never threw it out because, well, you never know when it will come in handy. Also I never throw out something that promises to keep me warm in winter and or cool in summer, is why I have stuff from 1980 still.
It works very well. The one difficulty is that I sleep on my side with a pillow tucked between my knees, which is hard to do with a floor-length nightgown. OTOH flannel not playing well with flannel means it does ride up, just enough to keep my pillow in place. I suppose it will do.
