I'm sorry I can't provide any comparisons with the S-Class. One thing I want to mention is an option on E-Class (W210) known as multi-contour seats (sometimes called orthopedic seats). Each front seat has several bladders which can be inflated/deflated to provide a custom fit. If you have any reoccurring back problems, I would suggest checking them out.

BTW, you can tell if a car has them by the large black control pads w/sliders just in front of the seat belt receiver (on drivers side).

Good luck.