Seadek is the company I got mine from... I got the small sheet in the 5mm thickness. The small sheet is a little short and too wide, so I just cut it in half, applied from the ends inward and used the excess to fill the gap in the center.
It works great for going barefoot, but I still tend to wear shoes anyway... just a preference thing I guess. I figured the foam would be better for those in the boat that just want to try out skating.
Here's a link to what I bought. http://www.seadekstore.com/index.asp?PageAction=VIEWCATS&Category=5
Hope that helps.