We have found these lovely foam seat pads at Swift Racing. They come with a velcro-ended strap so you can keep the pad on the seat even when the boat is on top of your head ... no more watching them float away!
We think these are the best around - not too thick - they are about 1cm thick - (which can make you need to adjust the height of your riggers), not too thin (so you feel the benefit), not held on by willpower (so you can use it again and again) and not too expensive!
The pad measures approx. 29cm x 18cm at the widest point.