The only way to comfortably sleep on your stomach is to (1) put something (small) under your hips to elevate them if necessary...but the all important #(2) is to put a small pillow under your calves. This will relieve the pressure off the small of your back. Do NOT use a pillow for your head (unless you have it under your forehead so you can breath during the night....I used to hang my nose over the edge to accomplish that.
Best thing....find another comfy and favorite position. Laying on your stomach is one of the worst for spineys. But is done often because that is the position you need to be in for back massages.
Using pillows to support your body is quite important to a good night's sleep. Keep trying different things until you find the right combination. Good luck to you.