I have a 3 layer SleepEZ latex mattress, purchased this March, and for most of the time it’s been perfect. The best mattress I’ve ever used.
Lately I’ve noticed that the middle area that supports my torso sinks down several inches below the sides when I apply the same pressure to both areas. I don’t know if this is normal or a manufacturing defect, but it’s not nearly as comfortable with a valley in the middle.
Assuming there is no other reason such as the foundation … your mattress is about 3 months old so it will have been broken in (cover, wool, and foam) where you sleep more than the rest of the mattress so what you are experiencing is likely how the mattress will remain for the long term. The sides will eventually “catch up” but they would take a little longer because you don’t sleep there as often. I doubt that if you measured using equipment that used exactly the same pressure that the difference would be 2" (you can’t measure what is happening under your body accurately by eyeballing or estimating “same pressure”) but if it actually was a 2" difference based on more accurate measurements then this would seem a little large to me. Your could use a bowling ball or something like that to see if it really was 2".
What they normally suggest to test for manufacturing defects is to put the layer on a flat surface like the floor and then put a string across it to see if there is any unusual impression (they will tell you what their guideline per layer is but it’s probably about 1/2").