My DH made a rectangular board to fit over my ironing board. I covered it with one layer of batting followed by aluminum foil and finally a heavy fabric - don't know the name but it's smooth and could be used to cover furniture. Probably cotton duck. I didn't want my ironing surface too soft and the aluminum foil reflects the heat onto the bottom side of whatever is being ironed. The fabric is stapled to the board and I haven't changed it. Maybe in another ten years.
The whole things is firm and taut. I know the foil works because I have to move my small pieces around as the board heats up when pressing a lot of seams open.