Options are limited.
I don't understand why power boaters get to have cushions that remain in place while we have to put up with fiberglass butt. I used to come home from sailing races and my wife would ask if I was beaten by a bag of oranges. I know about sliding cushions being a hazard, and cushions being a danger to footing in the cockpit but jeez why do sailors have to suffer. On a six day ocean trip I was fine with the T-Storms, the seas, the lack of sleep, but at some point I just wanted something comfortable to sit on.
Closed cell cushions are pretty hard. Better than fiberglass but only OK for a weekend or less. I don't know why we can't do better.