I was having back pain problems with my current car (Audi A4 Sport, sport seats but no lumbar support). This was not due to the ride, as it's quite soft (no S-Line suspension). I finally worked out that I had the seat set too low. This meant that my legs were lying fairly straight from my hips, with not much of a bend in the knees. This must have resulted in increased pressure on my lower back when driving.
Raising my seat has created a more pronounced bend in my knees, and this has had a dramatic effect on my back pain when driving. It really has made the car so much more comfortable to drive, even if its soon to be replaced by a Golf GTI!
Of course, this might not work for everyone. Particularly taller drivers who may end up with their head stuck against roof lining if they raise the seat much (I am only 5'10").