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Besides the main pillow under your head ( and that is your personal preference, use subsidiary pillows as follows to comfort your spine:

For Back sleepers:

• Put a roll to support your neck. Or pull the pillow a bit under your shoulders.
• Put a pillow under your knees.
  This is best after back surgeries and attacks of back pain.
  

For side sleepers:

• Put a roll under your neck.
  
• Put a pillow under your arm 
  
• Put a pillow under you between your ribcage and pelvis.
  
• Put a pillow between your knees 
  
• OR use a long pillow to act instead of 2,3, and 4

For belly sleepers:

• Belly sleeping is the most stressful for your spine.
  
• You must abstain from it if you have back pain, injury, or after back surgery unless instructed by your physician.
• Here use the pillow under your pelvis, not your head.