There are none everything is uncomfortable, left side is optimal for baby but I find sleeping on my sides gives me intense hip pain even with a pillow between my legs it's just not comfortable. If im on my back I feel like I can't breath and also on my tummy I'm fining I have to prop myself with a pillow so I'm almost sitting up but leaning over on my side that's the best but I slip after about 10 min or so :(
Also as a disclaimer I'm 32+4 so you may find something is more comfy if your not so far along.
I love pillows <3 I usually lay on my side with a pillow between my knees and ankles. Towards the end of pregnancy I end up putting a boppie or small couch pillow under my stomach to help support the weight. If you have heartburn my friend swears by sleeping upright with a bunch of pillows behind her. Hope this helps :)