When you sleep on your side, the best way to support your head and neck is by taking a fairly thick but soft pillow, bunching it up, and then tucking it under your neck and head. Too thick a pillow will push your head to one side, and too thin a pillow will allow your head and neck to sway downward.
You can buy contoured pillows designed to position your neck, but they don't fit everyone exactly right, and they cannot be manipulated as you change positions. Any modestly thick and soft pillow that can conform to your preferred sleeping position will provide more than adequate and comfortable support.
Find out more about this book:Your Miraculous Back: A Step-By-Step Guide to Relieving Neck & Back Pain