You may have had or have one yourself. A car with seats that force you down and back - even when you are stationary, and not driving Mach speeds - not that you would, of course!
We had one of those cars at the worst time possible. It was just before my first hip replacement when getting in and out of the car was more challenging than usual. That's putting it mildly.
To counteract the enforced field of that car seat, I purchased this thin but firm wedge-shaped foam cushion. Since we weren't in the market for a new car, it was an improvised solution that leveled the seat and gave me a bit more height.