Extra firm mattress, hard to find these days because quality is very rare, you'd have to go to a good shop that still builds american. My last mattress was so firm that I had it for 20 years and it never even had any sign of use, no dents, compression, nothing and my back did great with this mattress.
Long walks or treadmill to keep moving.
Core exercises, Stability ball exercises.
Reverse Hyper Machine is perhaps the single best lower back exercise that I can think of because it addresses back stability which is probably the main cause of back pain. If you make the low back strong through this movement low back pain will be much less frequent.
Roman Chair......poor mans reverse hyper.
Belt Squats a safe alternative for traditional squat.
And don't forget certain medications can lead to back pain. Most people don't think about this, but I used to take Calcium Channel Blockers for blood pressure and screwed up my back. I get on line and research and there's lots of people reporting the same problem, some that even had surgery because they didn't stop taking this horrible med.