The Bottomsiders cushions were on the boat when I bought it. They do not have "hold-down" snaps but I think I saw on the Bottomsiders website that they are an option.
If and when I have to replace them I would consider the snaps. It's kind of annoying when you are hit with a gust and the cushion on the windward side, along with anything on it, slides off onto the cockpit floor.