Driver seat comfort
The seat shape,foams and adjustments ranges used in our trucks seems good quality and well engineered - for the average person.
My short answer is to change your seat angle and back angle a small amout for your drive each way. Do not sit on a wallet.
My long answer is based on years of working in the Office Furniture Industry during the "Ergonomic computer workstaton and seating" roll out during 1980, 90's, 2000 etc.
The office/computer chair design and testing specs (BIFMA, ANSI, HFS etc) can fill a file cabinet drawer.
Chair cushion specification is very complex but foam always will wear our eventually.
Your body shape and proportions will determine how well you fit the Toyota design criteria for the drivers chair.
If you think your seat foam is collapsed try sitting in new 4runners. If replacing you drivers chair seat is needed, I would search salvage vehicles that were totaled, maybe you can get a ready to install complete chair. You can use parts of it or the whole chair. Be careful with chair mounted air bags.