Hallway also has dreadful lighting but I'm liking the idea of a flannel sheet or something thrown over the shower curtain rod in the bathroom.... that has potential, I can either peer in from the hallway or stand at the toilet and look in the mirror at the reverse image.
Truth is, I try to design my projects so I don't have to do a lot of layout. I have a couple coming up though that will make that more difficult. I've been thinking I'll get two pieces of the white foam core, probably at the office store for a larger sturdier size than the dollar store, With the boards folded together, I'll duct tape it down. Then when it is open, use a permanent glue (not spray baste so will need to make sure I never confuse the two!) and cover both sides (leaving that wide opening) and then put down flannel, smoothing out from the center. Then just fix the edges with more duct tape, probably using a silly print one. That will give me a good bed width that can fold up and go behind the door. Still not ideal, but will be adequate for my needs.