Failing the purchase of a manufactured kayak pan seat, maybe retrofit a plastic school-classroom style desk chair? Drill off the plastic seat pan, cut the backrest down to below sheerline height, or lower with a back band, and mount that on a minicel slab.
Probably dumpster-bound free, and if you don’t like it after some test sits, try again with what you learned on the first try. Maybe something like this, leaving hinged platform with DIY cup holders. Gotta have cup holders.
https://www.webstaurantstore.com/fl...EqMr8D9hcGyYws5J6ylEr4fNtBKk9aExoCKlgQAvD_BwE
Another, more DIY alternative solution, might be to carve a slab, or stack of taller laminated slabs, of minicel, a la:
https://www.thefoamfactory.com/blog/index.php/why-you-should-make-a-custom-foam-kayak-seat
I recommend shaping the butt cheek depressions first. Drop your drawers, plant your naked arse cheeks on the minicel and trace your buttocks with a Sharpie. Slowly, incrementally carving and test sitting the cheek depressions with a piece of Dragon Skin. Carve a bit, test sit, carve a bit.
No sense putting your pants back on. Please make a tutorial video.
Then, again slowly and incrementally, carve the hull-conforming bottom shape. Pants optional.
Those stacked minicel slabs may lose an inch of butt cheek height, and an inch of base height, so something like a 6 inch tall slab of minicel might get you a seat raised 4 inches.
I know from past oopsies on a couple boats that the butt cheek seat “pan”, with a low seat height, needs to be tilted back an inch or so to be thigh comfortable.