Thanks a lot for the replies, much appreciated. Useful to build up a bit of a picture of what tends to work for people.
I'm not a runner or cyclist and I think naturally have pretty good hamstring flexibility. Hip flexibility considerably worse so stretch a fair amount here in an attempt to help with climbing. I've actually done more stretching and yoga stuff this year than ever before and have progressed a bit with it. Maybe that's lucky timing or else I'd be totally knackered. Some stretching feels good for the back, some I've felt like it's possibly made things worse (though entirely possible that's due to user error / doing it wrong). I do find I have very tight glutes when trying anything like pigeon pose or 90-90 type stretch so now wondering if that might be a significant contributor to the problem. It sounds like stretching does a lot for people so will re-double efforts here and try some new, more lower back focussed stuff and see if I can identify what (hopefully) helps.
I did...
