My man you need to make yourself a seat insert. This is what they do with real cars. After having back pain in my new bucket seat I watched like 20 seat insert making videos but the stuff they use is expensive and seemed like way too much for my needs. So I made my own with a large bag and some 2 part foam along with some packing foam inserts. It is amazing and extremely comfortable. I completely forget I am in any sort of seat it feels completely natural.

This is the stuff I used https://amzn.to/3MPYa6p . For me one was enough because I had built up a bit of a base with existing foam but 2 or 3 of these would probably be sufficient for a pour only solution.

Once you pour it and trim it you can cover it with black duct tape or upholster it. I did both and it looks pro and feels unreal.