I'm rebuilding an old bike seat and need some seat foam. Standard oblong shape (like old Honda CB350) with springs running longitudinally. Everything I"ve looked at around here is too squishy. I want something that's high-density. Anyone come up with any creative solutions for this sort of thing? I've tried the local medical supply shop but the stuff they had wouldn't work. One local upholsterer had foam but it was the thick stuff that compressed too easily. anything online?