I’ve managed a bad back for over 20 years – old rowing injury. These are the things I’ve found that helped:
A long bed (I’m 6’6”) so that your feet are supported;
Sleeping with your legs together (no jokes please!!)
Core exercises;
Sitting up at desks/tables – no slumping!
Keeping active (although it doesn’t seem like that is an issue for you);
Perhaps you should review your bike set up? Tiny changes can have a big effect on back, knees etc.
If it hurts – stop. Would be my best advice.