I sleep with a body pillow n like 4 regular size pillows n it helps a lot cuz I can only sleep on my side now
I sleep with a pregnancy pillow on my left side. Wolfeenix said it best ^^
Sleeping on your left side is the best option although if you alternate sides its ok. Sleeping on your back is dangerous to the baby as there is a vein that runs down your right side and laying on your back cute off the flow which can impact on bub and make you dizzy.
You can sleep in your back if you wedge something under your right hip to take the pressure off though.
I'm 34 weeks and I find sleeping with a body pillow helps a lot :) and having a bath right before bed helps relax you to fall asleep