I have a Mercedes GLS, but from what I've heard, other models also have this problem: headrests are way too far forward. I have to sit pretty upright due to back issues, and the headrest is super uncomfortable (pushes my neck forward.) The polar opposite of an ergonomic seat.

I tried 5 or 6 different pillows and supports, and finally found one that helps. It basically pushes my upper back slightly forward so that my neck can rest back on the headrest (rather than the headrest pushing my neck forward.) It leaves my lower back alone so I can sit in the seat properly and use the built-in lumbar supports. It also allows my shoulders to rest where I like them (in line with my back rather than hunched forward.)

Since it's a two-pack, I used the second one in the back for my son. It's way better than the wonky back headrest (which is even worse than the front seat ones!)

Hope this helps! Although the real solution is for the car manufactures to put the headrests in a proper position.