Hi photocat,
Regarding a “bump” in the middle of a split latex mattress, that would be odd (as you surmised), as all the layers would be the same thickness (or have a very slight difference). To help try to determine where this might be coming from, I’d first start with the type of foundation you’re using and make sure that it is not contributing to the sensation you’re feeling. You can place the mattress upon the floor as a reference if you have the room.
The next thing I would do is start from the beginning and remove all of the layers, making sure that your mattress encasement is flat underneath. Then place the first layer in, putting a few “waves” through it to make sure that it is not overly stretched or compressed in one area. While it sounds simple, Do the same with the second and third layer, and make sure when putting the “waves” through each piece that it lines up both length and width-wise, and that where it meets in the center it is not bunched too tightly, as latex is grippy and has a high coefficient of friction. Also, make sure that each layer Dunlop layer is facing with the same side up (you can tell the difference in the 3” mold pieces of Dunlop that Savvy Rest uses). You can place a sheet over the latex after you have the first two layers together to see if you feel the “bump”, and do the same thing when you have all three layers assembled, and then test it again with the encasement zippered on top, attempting to logically diagnose if you can find the source of your complaint.
There will be some breaking in of the product, mostly the covering, during the first few months, but otherwise the latex won’t change too much during that time. As far as the difference in length is concerned, Savvy Rest cuts all of their pieces at their facility to control dimensions quite tightly, but it is very easy to have a layer 2”-3” longer than the one next to it if it is stretched slightly, which is why it is helpful to put those waves through each layer when getting them aligned.
I’d perform those diagnostics, starting with the foundation and moving up from there, to see if you can wither find the cause of your discomfort, or “fix” it with reassembly. If you still have a problem after that, and after having given the product some time while sleeping upon it, I would phone Savvy Rest directly, as they are quite helpful to their customers (they are a certified B corporation).
Phoenix