Use the rubber pads under the resin diamond discs. They have PSA on the back and you stick them on the plastic lap. You stick the resin diamond discs on top of the rubber to make the sanding process more smooth. I found the rubber pads at Kingsley North for less than Ameritool and there is a quantity discount.
http://www.kingsleynorth.com/skshop/product.php?id=46556&catID=187Smoothing discs go from 220 to 3000 grit. Don't know if you have an 8" or 6" machine, but here's the link for the 6" discs:
http://www.kingsleynorth.com/skshop/product.php?id=97048&catID=109Eastwind makes high grit polishing discs, but note they are expensive (but really good):
http://www.kingsleynorth.com/skshop/product.php?id=46659&catID=182You can use silicon carbide wet/dry sandpaper, but I've never used it. Somebody else would have to tell you what to get in that department.