I know it's hard for many people to do, but I trained myself to sleep on my back with a good neck support pillow - don't know a specific name.

Pillows are really difficult, and they have to be perfect. That is because they will strain muscles, tendons if they are only a bit too high or low, soft or hard, because you stay in the same shape for so many hours. I liked a thick memory foam pillow. But we bought a hybrid bed and I sunk into the memory foam more, and the neck pain was getting worse and worse. I went to a very shallow feather pillow, and it has helped. But if my neck gets bad, I go upstairs and sleep on a hard bed, with the memory foam pillow, and wake up much improved. So it also depends upon the bed!

As for retraining to sleep on the back, not so much! I was always put on my side or stomach as a baby, and no matter how I go to sleep, I wake up in those positions. I notice my grandchildren, who spent their early years on their backs, all sleep in their backs. That was supposedly to stop SIDS but it looks like it will be a benefit to their backs and necks as they grow up!

I am brand new here, but wanted to comment on this. I have had constant issues with finding the right pillow - for all the reasons you describe. I went from a standard pillow to a memory foam pillow to another memory foam pillow to a wedge pillow. I finally found one by a company called OMI that has a buckwheat filled, wool-lined pillow that is perfect. It is heavy, and expensive, but it is delightful. I would highly recommend it.

This the style I use:

https://www.amazon.com/Hypoallergenic-Orthopedic-Cervical-Removable-TAMPOR/dp/B01LWUBAKH/ref=zg_bs_3732111_14?_encoding=UTF8&psc=1&refRID=76R5NHWA44GVYXX8SGDR

Memory foam "contour" pillow. I use Serta brand, sold at Menards, just as good as pricier ones sold in department stors. Good for both back and side sleepers. I have had 3 neck fusions so my neck is very fussy. I will never go back.