Thank you for all your answers.
The McKenzie Therapy - concept sounds promising, I will look into this.

Kathi your back really sounds a lot like mine, and I too experience pain relief with a pillow between my knees (which I found out by accident not long ago). Thank you for the link, really helpful information!

And yes, I think the tightness of the hamstrings could be related to the back issues. Stretching is my weak point in general... I just hate it to be honest but will have to get back to doing it regularly.

I think I will give things some time to settle while working on my own and then give it a try with another PT.