There is a board in the flooring area at Lowes or HD. I can't remember exactly what it is, but I think it goes under some flooring. You can get it in 2 foot square or 2 foot by 4 foot. It's sturdy but much lighter and thinner than plywood.
I made slip covers for my ironing board. The inside is made of towels and the outside is some cotton home dec fabric. I modified a pillowcase pattern for the outside. Jenny from Missouri Star has a video on YouTube that explains the whole process.