Canoe seat recommendations needed

I have been pouring over the internet looking for a suitable canoe seat for my Grumman square back canoe. I am around 250 and have a bad back. After about 30 minutes, my back starts screaming without any kind of back support. I always sit in the rear of the canoe and it doesn’t have a typical bench type seat, but rather is wide flat surface. I cannot find a decent canoe seat that would attach to that kind of canoe seat. I prefer to not drill holes in my canoe, but if necessary, I would if I could find a good seat that would work. I also run an electric trolling motor on the back that I need to be able to reach.
Here is the best photo I have of the canoe seat that I would need to attach the canoe seat to. As you can see, there is no way to get any straps or hooks around that. If you have any recommendations, let me know. I thought about one of those swivel seats you find in a lot of boats, but I would prefer something more compact and removable if possible.

One thing you could do with one of those swivel seats, is mount it to a wooden framework that plops down over the existing seat. Blocks extending a short distance down the front and back sides of the existing aluminum seat would keep the framework from slipping out of position. The main part f that framework could simply be a piece of plywood having the same shape as the top of the existing seat.

Here are a couple more options for your consideration. The chair is a Crazy Creek.

You can keep it simple. Something like this, in conjunction with some kind of foot brace……0…1c.1.64.psy-ab…0.4.269…0i22i10i30k1.0.hMx5nUvTLiw