I like my ironing board to be flat. I don't use batting. For my regular ironing board (the scissors kind) I use denim or really heavy cotton fabric (I think it is called 'duck') in a medium color, so it doesn't show dirt or burnt on starch. This can be washed and put back on.
For my home-made wooden board that is 32" x 24", I put down a layer of Insulbright and then cover it with denim or a heavy cotton. This is stapled to the board. However, next time I will make one and put a cord around the edge so that I can gather it up and then be able to just untie it and wash it and then put it back on when it gets dirty.
The reason that I don't use batting on my boards is because I feel that blocks iron much flatter when there isn't any puffiness on the ironing board.