Definitely use pillows. At least between your legs. Even with my first I couldn't really sleep on my left. It felt so much more comfortable on my right. Honestly getting
sleep is more important than which side. Tossing all night to get comfortable isn't going to help the baby. And if the way you are laying is effecting your baby, your body will tell you to move. I occasionally lay on my back, but for me it is comfortable when I put something under one side to lean. I've never been one to sleep flat on my back.
I've also been having pregnancy insomnia I can fall asleep but if I wake up I'm awake for hours. I want to stretch out also and I do! They say to sleep on yorbkeft because it has optimal blood flow to the baby. I have a lot of cushions under my knees one at my back. I build a fortress around me lol