It can take some time to become comfortable sleeping on your left. Sleep with a pillow at your back or between your knees to prevent rolling. If your partner is on board, you can also try moving to the opposite side of the bed. It forces your brain into deciding again which side is “right”, and it will be easier to form a habit of sleeping on the left.
Sleeping on your left side has many advantages. It may be the secret to rejuvenating sleep that you have been missing.