I'm not sure if you found our Better Bedding and Mattress Sales Series, but if not, check out...
There is a lot of information there on mattress materials. Check out specifically "Bedding Anatomy 103" and search for the term "body impression".
I would also purchase David Benbow's book "How To Win The Battle For Mattress Sales" and Gerry Morriis' book "Sell More Beds, Guaranteed".
My take on the upholstery laters is this... lesser quality materials or materials that shift will negatively impact comfort over time by making body impressions more likely. Also very thick mattresses with lots of upholstery layers can be more prone to body impressions.
Please let me know if this helps.
Regards,
Russell
Russell Bienenstock
Editorial Director
Furniture World Magazine.