What Should I do to make my lower back and butt comfortable on my sit-on-top Kayak.?

I’m a kayak fisherman with an sit-on-top Emotion fisherman kayak. I have a cheap seat and I have tried a $100.00 seat before which I took back. While I fish my lower back gets sore I’m sure a more expensive seat will make my butt comfortable but my back needs support, maybe its the way I sit but I usually shove something behind my lower back to act like a lumbar in a car seat for relief. I’m 6’0 tall 215 lbs thick athletic build. All the seats I look at don’t seem to have any kind of lower back support. I usually quit fishing because my back gets so tired so any kind of advice would help. Thanks for your answers.

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I am 6’3″ and 235. What Kayak should I get?

My friends will get the cheapest kayak some where like Dick’s Sporting goods. ($200-$300). I am willing to spend a bit more (around $500). We will mostly be on lakes (Fishing) and a float trip every once in a while (slow Missouri rivers).

I want to be comfortable and safe. I want to keep up with my friends who are all under 200lbs, so hopefully it handles well. I sat in one at Bass Pro that seemed nice. It is the Ascend FS10.

Any opinion would be appreciated. I am new to this.
You guys have got me thinking. What Canoe would you recommend. We like to each have our own boat, so what Canoe will be easy for one person to handle, but can hold two if needed from time to time.

I am still leaning towards a Kayak though. Does anyone have an opinion on the model I mentioned?

Thank you to all.