Easy, cheap design wall: Next time you pass one of these places where they frame pictures and paintings drop in and ask them if they have foamboard sheets they could sell you. Ok, not the foam we are used to, but actually encased in a plastic coating. And some places that mount posters have the sheets with a self adhesive side to them. Get the size you need. I got the biggest one available: 1x2meters. Adhere flannel on the sticky side, or tack the flannel with some spray glue and fold the excess fabric around the edges.
This material is so light, you can easily move your design wall, it’s thin enough it can slide out of sight behind a bookcase, and is thick enough (1cm) to be able to use pins for bigger pieced blocks.
*This tip submitted by Valentina P. Thanks Valentina!