Best way to sleep with low back pain?

To lessen pain. Your body will typically tell you how to best sleep. Find position of comfort and try to rig a way to keep in position. A lot of people find laying on their side with pillow between knees and one behind back and in front of chest to prevent them from turning onto stomach or back.
Bask. On your back with a small pillow on the lumbar/loin(lower back) area.