Hi Azalia34,
Welcome to the Mattress Forum! 
You’re very welcome. 
Many people do prefer the ability to test items and different configurations out in “real time” to help minimize some of the “guess work” that can happen with some online purchases.
You may perform a forum search on Berkeley Ergonomics (just click on the link) for more information about them. They use natural Talalay latex from Radium and other good quality and durable materials, and I do think highly of their line of mattresses.
This is a common question (and a long answer). Let’s use the example of a single core of say 6" vs a “split core” of 2 x 3". When core layers are “split” it reduces resistive forces inside the layer itself. When a foam layer is compressed … it affects all the surrounding material that is attached to it. The material below is compressed and the material beside the compression point is stretched and pulls back against the compression (in addition to the resistance of the foam below the compression point). This creates various interacting forces inside the mattress including shear forces. When a layer is split … it reduces these “resistive” forces and the 2 layers can react a little more independently and act as if they are slightly softer and you will sink into them a little deeper. Having said this … if the ILD of the two 3" layers are the same as a 6" layer and there is a comfort layer on top of them then most people wouldn’t notice a difference. In the same way a comfort layer that is made of three 1" layers of say 19 ILD will function as a “softer/thinner layer than a single 3” piece of the same ILD but in the top layers and with thinner layers the difference would probably be more noticeable. Because of this … in “theory” a single core can be a little firmer than 2 half cores of the same ILD although the difference probably won’t be large enough to feel.
Also in “theory only” … two 3" layers that were exactly the same ILD as a single 6" layer could be less durable over the course of a long lifetime because they will act more independently and abrade each other slightly but I don’t think that any difference would be significant or even measurable in “real life” terms and the other factors that affect durability (see post #4 here) such as the firmness of the layers would play a much bigger role. It certainly wouldn’t be a concern of mine.
Multiple layers would have more options for fine tuning though both before and after a purchase because for example a support core with a medium over firm layer would be a little firmer than a medium layer and a little softer than a firm layer (closer to the medium) and you would also have the option to rearrange the layers to firm over medium which would still be in between a medium and firm 6" layer but closer to the firm. You could also use the softer top layer in the middle to create a firmer feel compared to having the soft on top. The main advantage of having more layers in other words is that for those who need it can provide more options to customize the layer combinations either before a purchase or by rearranging or exchanging layers after a purchase. While this is attractive to some people … it can also add some complexity that may not be necessary or may not justify any extra costs involved in having more layers for others.
There are certain circumstances where a single layer would be an advantage while in others … the ability to choose a firmer “bottom half” of a lower layer can also be an advantage. One is not better than another as long as it can be “predicted” how a particular construction will respond in a reasonably accurate way. In some cases the differences are so minor that they do not play a significant role.
Overall, outside of a mattress with more layers having more options to customize the mattress, if a mattress is a good match for you, then one isn’t inherently any better than the other.
Some people prefer the look and the ease of handling (latex can easily be torn and is “sticky”, having a high coefficient of friction) of a covered layer of latex, and in theory the extra covering could offer some extra protection against abrasive forces and extra UV and oxidative protection. On the other side, this does add a little extra cost to the latex layer, it “may” slightly impact the point elasticity of the latex, and the layers “may” slide around a bit more and requite more frequent repositioning. I spoke with one larger manufacturer that covers their latex with cotton, and they stated their number one reason was that it hid and cut down on questions about the variations in color and the natural voids/inconsistencies you can find in a sheet of latex. So in the end, it would be mostly a matter of personal preference.
Phoenix