I use a towel folded into quarters. I dont think tamping is really going to damage your benchtop that much. If youre really concerned, hit Clark Rubber to get a mat of some sort. You can even get pretty thick mats at Bunnings, but you buy it off a roll, so youre probably going to have to get at least something thats like 800mm wide. You can make like 4 mats from that if you wish.
Another idea is to sniff around carpet places to see if they have any off cuts of padding. Dumpster diving! :P