Honestly though I have the 30x30 pad and I wouldn't want it to much smaller so a 28 is really the smallest you want to go. If you just get the $30 wool felt pad that is 1/2in thick you can actually cut it to fit. Pretty easy. That way if you want an extra inch off or you want it more contoured you can custom fit it. The wool wicks moisture away so much better than anything else.