What a big bunch of great ideas! Everyone is so clever!
I'm actually trying to make a design wall today, using a method a friend told me about: buy a piece of 1-inch thick styrofoam from Lowe's, they will cut it to whatever size you want. Get it home somehow. (My friend's wall is big, about 5x8 feet). Prewash enough flannel to cover in your choice of color. Iron it. Get somebody to help you stretch the flannel around the foam board tautly but not too tight, overlapping it at least 10 inches to the back. Duct-tape the flannel snugly to the back. If you have a sewing room, attach it to the room's wall however. If not (like me) find a storage place for the design wall and haul it out as needed. I need a large one that can be moved in and out of my dining room, my only place to sew. We'll see how this works out for me.