You see diagrams like this in most mattress literature,
all claiming to provide correct spinal alinement and pressure relief.
The truth is you have to carefully line up the proper mattress with each individual, and to complicate matters even more you and your spouse often have different needs
Most of the time one has more pressing needs while the other is more flexible and
find they a suitible mattress for them both.
In some case each person has pressing, specific needs in terms of pressure & support. For example: We can offer each partner a different comfort level on their "side of the mattress".
Or 2 different mattreses in a king or queen size adjustable bed, or simply provide different padding on each side of the mattress.
"Your mattress your way"
General information that may be helpful.