As an addition: I solved my back-problems by getting rid of my pillow (I think switching to a really thin one also helps). The first days are a little bit uncomfortable, but then it’s actually quite nice and I sleep more often on the back or stomach, instead on the side. Definitely worth giving it a ~10 days try!
Data point: After reading this comment I tried this for like two months—initially intentionally, but also the pillows I had at the time were not right for me and so I kept doing it because getting the right pillow can take a fair amount of time and money. It actually significantly increased back and neck pain for me, I think because my tendency to sleep on my side is just very very strong.