The best sound absorbing mats are those which have interlocking edges and are about 5/8" thick of a closed cell foam. These are also nice on the feet and can be cut to fit the boat's floor--plus are cheap. Mine came from Sam's club (on the 22).
However, I don't like to let my boat pound, and don't have any mats on the 25. Pounding is abusing the boat. It may not show up immediately, but in time, it can loosen screws, and the bulkheads (not sure if the most recent boats have glassed in and molded interior, but I would feel the same way). I grew up on a boat which had a bottom very similar to the C Dory, and my father drilled into me--do not let the boat pound. Put the bow down (Permatrims help) and slow down, or take a different tack. Quarter into the waves.