I am limited for space, so for my design board I purchased a plastic table cloth at the dollar store (get the one that has the flannel backing on it). I then put three grommets along the shorter side (button holes made with your sewing machine would also work, or just sew several times in a circle till it is strong). I then put 3M command adhesive hooks on the wall, hang the table cloth (plastic side toward the wall and flannel out), and there we have it.
If someone is coming over I can unhook, fold it up and put it up next time I sew.
I will admit that there are times when I wish the flannel would hold better, but it is only the bigger pieces that fall off and I have learned which ones I need to pin up, and which ones will stick.
It is inexpensive, portable and works.
You could do the same thing with hanging up a flannel sheet, I think.
Hope this helps.