Tried propping a firm pillow behind my back every time I sat down. It kept me from sinking into the same soft spot. I also made a habit of flipping the cushion over every Sunday. The flat side slowly filled out after a few weeks. Now I don't lounge as hard and my couch looks better.
Wait, you were sitting cross-legged on the floor for HOURS? How is your back not just a permanent question mark shape by now? That's some next-level dedication to a game.