I'm 26 weeks and three days into my first pregnancy. I've always been a stomach sleeper. I slept on my stomach until it was uncomfortable and now I sleep with a million pillows left or right side doesn't matter. I seem to get heartburn if I sleep on my right side but nothing some tums can't fix.
I like to lay on my back also. I use my maternity Pillow under the right side of my body it feels like I'm laying on my back but I'm propped Where I'm turned more on my left side.
Sleep however comfortable. If the baby was in distress, you'd feel it you'd be uncomfortable or have shortness of breath and change position anyway. Try laying in your back with pillows propped behind you so your at an incline. You may still wake in night but the sleep you do get will be comfy.