It’s better to do balancing exercises after getting out of your car than changing the angle of your seating. The Standing Sacral Release is an excellent antidote for long rides in the car.
If you lift your buttocks up on a pillow or towel in the car and then need to stop suddenly you will be thrown into the steering wheel. The bucket seat is a protective angle to reduce this during sudden stops at low speeds.
You can sit on a deflated therapy ball, the 9″ small size, when it is placed front to back (like a menstrual pad) and allow your sitz bones to remain on the seat of the car.