I bought a special cushion for my car....and one for my computer desk chair....that has a cutout so that your tailbone "floats" in the empty space and your weight is supported by you a$$ cheeks. Works great for me.
Also, try going to a pilates class. Strengthen your core muscles, and your back will get better. I used to have really bad lower back issues, not any more.
Go ahead.....call me a homo for doing pilates.
14RF SUX