I have a 2" double and a 3" single. 3" is significantly more comfortable. Especially on the shoulders when sleeping on your side after long days of rowing. The foam used is different, too. The 2" is hard foam, the 3" is soft foam. My next purchase will be 4".
"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain