Hi sideways,
There are many forum members that have purchased one of their component mattresses and a forum search on SleepEz (you can just click this) will bring up hundreds of posts with more information and feedback including many of the members here who have either re-arranged the layers or done a layer exchange to fine tune their mattress.
This type of mattress design is very flexible and allows for many different combinations that can be fine tuned (or even used to make larger changes) both before and after a purchase. The only caution I would provide is to make sure that you handle the latex carefully if you are putting the mattress together or re-arranging layers because if you “pull” the layers or grab a handful and tug it can tear easily and it’s best to “wave” the layers into position and not pull on it.
If you aren’t able to test either a specific mattress or a mattress with a very similar design in person (same type, blend, and thickness of latex layers in very similar firmness levels with a very similar cover) to use as a reference point then a more detailed conversation with the manufacturer (in this case SleepEz) is the best way to decide on the initial choice of layers that have the highest odds of success for you (see mattress firmness/comfort levels in post #2 here). Knowledgeable and experienced manufacturers like SleepEz will know more about their own mattresses and which configuration will likely be best for you “on average” than anyone else.
Split layering is also a great option to have for couples who have different body types or different needs and preferences (see post #2 here).
As you probably know … SleepEz is one of the members of the site which means I believe they compete well with the best in the industry in terms of their quality, value, and service and they will work with you as much as necessary to make sure you are happy with your mattress.
Phoenix