@sweethighland
This is the wedge pillow I bought on Amazon:
Ebung Body Positioner - Premium Memory Foam Wedge Pillow for Sleeping, Sitting, Snoring, Heartburn Relief, Pregnancy, TV, Reading, Backrest, Leg Rest
Visit the Ebung Store

I now put 2 regular pillows on top so that I sleep more upright. Both go across horizontally, one supports my head.
I don’t slide anymore. But I don’t move around much when I sleep.