So I fall asleep for 28 years as I want. Time on the side, half encouragingly belly or back on the other side. And I've often one arm under his head and 2-3 different pillows. The huge mess I've now replaced by the single neck pillow. The first night: Horror. Although no back pain but getting used to was really huge. Second night: That's better, and now I'm totally happy for several days. Sleep better, have no more neck pain and I feel good to be "right."
So accustomed to anything new is stupid but then totally great.