I didn't like the lower back support in my W210, but I don't have the back issues you do. Even my Dodge minivan and VW have better seats with adjustable lumbar support.
There are some orthopedic seats with more support features (like these
https://www.ebay.com/itm/1996-2002-Mercedes-Benz-W210-E320-E430-E420-HEATED-ORTHOPEDIC-leather-seat-FRONT/191666342327?hash=item2ca03449b7:g:VosAAOSwd0BV0rL7)
but I'm not sure what else they need, like control units or vac/air hoses.