Okay, if you are really lazy, like I am, you could just use safety pins to fit the top fabric on the ironing board, as that is what I did. I also didn't want to mess with elastic, neither sewing it directly on or making a facing to slip it into. The safety pins work fine, and it is extremely easy to change fabric when I want to.
My ironing board top is 20 inches by 60. It is wood, cotton batting, and regular cotton fabric. The fabric I currently have on it is a purple flower print. I have used this board 8 years with no warping or any problems. I like having my ironing board top match the other purple things here in my sewing room.
Dina