A healthy pain free back relies on maintaining the normal curves of the spine.
Your lower back should have a small inward curve in it, almost all the time. Unfortunately, when most people in western society sit, they flatten out this lower curve and thus disrupt the normal spinal mechanics. Couches, car seats and most chairs actually encourage this incorrect spinal posture. The lower the seat the more likely you are to sit incorrectly. Ask your physiotherapist to adjust your sitting position so that you are confident that you are doing it correctly.
Care with your lifting technique will also minimize injury to your lower back. By maintaining the curve in your lower back as you bend from the hips and knees you will insure that your leg muscles are used to lift the weight rather than your back muscles. Ask your physiotherapist to check your lifting technique a many people don’t lift correctly….make sure you stick your butt out behind you as you bend over so that your body is angled forward NOT vertical!