I have a quater of a sheet of plywood. I covered it with batting and muslin. It sits on my ironing board. Yes, sometimes it could be a little more stable, but it is removable and I can take it to quilt retreats, set it on the table, and basically iron whereever I want to. I have thought about putting stabilizing blocks that just fit the ironing board, but it is not so unstable that I feel that I have to.
hope this helps.