My previous motor was a 55 reg SE 320i with std seats and always driving with seat back upright, I had very bad lower back pain which caused referred pain to my legs.
I now have a 59 reg 320D M-Sport with sports seats, lumbar support and heated seats. The seat back, I tilt back at quite an angle to take some of the weight from my lower back. It has made quite a difference
My back pain has now vanished and I now have no problems. A tilted seat back plus the sports seats etc. certainly works for me.