K.T.
Sounds like you're on the right track....I had a contour changing pad (they can't roll off) and the firmest mattress I could get (my mom bought it). I made changing pads that I put on top of the contour pad cover. They were two sided flannel with an inside of vinyl (the fabric is sold by the yard) - just buy a yard and a half and make squares (for travelling) and rectangles (for the changing table) - no need to finish the edges.