When I saw several threads on similar subjects, I was skeptical. How could Toyota, a car company which usually gets all the ergonomic details so right, create a seat which is, simply put, unusable? And yet, it is. After only a few weeks, and in spite of loving everything else about my 2008 model, I HATE the seats. My back hurts all the time, and I have NEVER had such a problem before. I have ordered one of the mesh type lumbar support things from the States. I'm willing to invest in the seat extenders if I have to (at 6' 2" I fit, but it's a little tight). I'll even consider the Wet Okole seat covers with lumbar support. But, Dear God, how did they design such a torture rack and then keep it for YEARS? I don't want to get rid of the car, which is wonderful, but I will not live in pain just to drive it. Any and all suggestions short of surgery are welcome!
I suspect, but have no data to back it up, that all seats have some segment of people that the seats won't work for. I have some fairly serious problems with multiple discs in my back, and am 6'-1" tall, yet the Prius seat works great for me. A few years ago I used a Lexus for a weekend road trip and no matter what I did could not adjust the seat in a way that didn't hurt my back. This is no help to you... Unfortunately IMHO if you can't get the seat to work for your body you're better off getting a different car. Your health should always be top priority.
I am 6'4" and had the same problem as you. Never had a back problem in my life and after a few months of driving the prius I had a bad herniated disk. What solved my problem? Had the complete seat moved back 8 inches by means of a custom fabed seat mount, the existing mount fit into. Within six month of the of the change, my back is back to normal. No more herniated disk...no surgery...which a well respected Neurologist insisted I needed. Also tried all sorts of lumbar supports before doing the seat mount, nothing made a difference. Scott
Cycledrum seems to have fixed his seat problem. I would suggest looking for his writeup on the subject and/or send him a PM.
The Obus Forme seat thing works for me. I hate riding in my wife's car without it. I got both the back support and seat cushion.
I agree that the 2G Prius driver's seat won't win awards for comfort. Perhaps you may be interested in this string: http://priuschat.com/forums/gen-ii-prius-main-forum/58247-i-added-new-handle-08-a-2.html