The important half of we has a favourite pillow. It goes with us when we travel as every other pillow is not quite right. Agree most motel & hotel pillows are useless as sleep aids.
In the real world Pillows might need to be more than soft, medium and firm.
The science is less clear. Some one suggested you need to keep your spine straight if you sleep on your side. So there may be a height/thickness need that varies. I tend to use my body to change how much support a pillow gives be tucking my arms under. Some one suggested this is not good and I might suffer circulation issues. The same some one said by observation I don’t sleep on my side. I sleep in an odd position according to non science. So it’s not that the pillows are wrong, it’s me that needs to change to sleep like some one else. Perhaps it also matters if a bed is softer or firmer or plush as to how much your body sinks relative to your head on a pillow. Perhaps because I sleep non scientifically I need to adopt a scientific pose relative to the bed. And then I will be able to sleep.
To think all these decades it’s not the pillow or mattress that is to blame for poor sleep. It’s my fault for not sleeping per the design requirements of the people who made my pillow and bed.
The same someone suggested the $6,000 mattress would be a better one to sleep on than the $3,000 one I was trying out, and that there is a $200 pillow that is just perfect for me.
The first bit of science needs to answer if there is a right way and wrong way to lay when sleeping. Think tatami mat, fouton and timber or carved stone neck rest? Definitely no pillow.
It’s a great question to ask?