Its best to sleep on your left side being circulation is better for the baby the doctors usually say not to sleep on your stomach with my first 2 pregnancy I slept on my left side slightly turned on my stomach and found it comfortable a pillow between your knees will help with comfort as well
Not sure about harming baby, I just imagine it would be extremely uncomfortable for the both of you the farther along you get. I'm 34+3 and I can't imagine sleeping on my stomach! Hope you find answers!