Take a look at the Tahe Kayak Backrest at S2AS!

Foam covered seat and back rest, comfort and support for your back, easy adjustment.

Tahe's backrests improve the paddle comfort of Tahe kayak seats, and are absolutely indispensible for long distance paddling. Aside from the improved comfort, they also help increase your paddle power, keeping the back well positioned in the lumbar region. There's nothing else that can match it on the kayak market.