I switched from a Benz to the Volvo S70 because the Benz seats aggravated low back injury pain, and the Volvo made it better (but I drove the Volvo first, to make sure). However, the Benz had a headrest which could be rotated froward as well as having height adjustment, so I could drive with it right in the curve of the back of my neck--much more comfortable for the neck. I don't recall if the spacing on the Benz headrest pillars was different from that on the Volvo or not--if you are tall enough that this might work for you, check the junkyards for the right headrest and measure to see if you can just make a straight swap.
On days when my neck is bad, or I'm on rough roads, I have a cylindrical foam Pillow on a loop of elastic that I can hang over the headrest and twitch up and down as the need arises.

Alternatively, check out any other Volvo you can get your hands on, to see if there is a Volvo seat that fits you, then hit the junkyards and just switch the seats! (I recently replaced the bench seat in my pickup truck with Volvo seats--had to fabricate mountings, but well worth it.) For most Volvo seats, you shouldn't have to do more than remove the bolts and wiring. I got the seats from Brian Leppin, a Volvo recycler who gave me a good price on exactly what I needed. bleppin@erols.com
There has to be a solution somewhere that doesn't involve ditching the car!
Good luck