Thank you so much for the information, I hugely appreciate it! I wish I lived somewhere where I could just go sit in a bunch of old ones - it's so hard to know what will be comfortable just from photos! I'll maybe talk to my mechanic again and ask him if he'd be up for modding a bit if needed - he normally only does engine sort of stuff but said he'd be happy to help me if I found a seat. I'll try looking at just the bottom parts too, I never would have thought of that! It was driving me crazy because all my online searches just kept showing me seat covers instead of actual seats so I had given up for a while, lol. Back to it I guess!
Thanks again!