If you'll be ironing on it, cover the wood with heavy duty aluminium foil so steam from the iron doesn't warp the wood. OSB is prone to warping from water/steam. I've used foil then a layer of batting then ironing board material for the top of my wood and it works wonders. one layer of batting is soft but still will allow you to put a cutting mat on top and cut easily so you have a two-for-one surface.