Im not sure if putting a pillow under his head is wise because baby's arent experts on anything but I would be worriedthat the baby would need to swallow some saliva or the bend from the pillow would mess with his breathing. You could raise his mattress if he is in a crib and even if he is in a bassinet you can still put a pillow or couple of blankets behind the padding. i do agree with the wedge around him.
I didn't do the research as the other mom did but i do know that there are some tricks to helping baby's sleep. Your son knows your voice and your scent. He's known ever since your first time you held him. My son use to be in the hospital and the nurse advised me to sleep with the blanket I wanted to put my son in and that way he feels that I'm there. My daughter she is now to big for her bassinet now but I think it made her feel snug. It was a smaller space then a crib. I just got up and looked right over the edge and she could see me.
It ranges from the familiar noises that could help your son sleep. The CD's that have the heart beat on it or the nature CD's with the noises with the ocean. Constant sound of the waves on the beach. IF constant noise helps him sleep. Wrap him snug and get a wedge. I use a big medium thick blanket for my size of bed (full) and i wrap it up and loop it around my daughter. IT and the snug wrap I put her in makes her feel that im holding her.
Also call your doctor, join a support group, and would a humidifier work? We have a humidifier that was made by Vick you kow like Vick Save and it works so well. Even helps me out. I wish you luck.