I sleep on my side, but I found that the only pillows that I can sleep on now are my Mediflow water pillows. I have 2. I don't stack them, I sprawl on my queen sized bed and either sleep on 1 or the other, depending on which is more comfortable for the night.

One is filled with 2 liters of water, the other with 3. So they're a bit different (2 liters is 'softer') to accommodate whatever I feel is more comfortable any given night