Hi marshmallow,
There are a number of local or online manufacturers that will customize the base layers in their component mattresses but it’s more common with latex base or transition layers than a polyfoam base layer. There are also many that allow you to exchange your layers as well after a purchase (sometimes just the comfort layer and sometimes any of the layers) so you can fine tune either the comfort or support (or both) of the mattress based on your actual experience. Some of them also have a good return policy if none of the configurations they offer works well for you because with more challenging circumstances or weights “theory” may not agree with your actual experience in terms of PPP. A list of many of the better component latex or latex hybrid options I’m aware of that are members here is linked in the tutorial post.
Just for reference as well … the Comfort Max 400 is described as having a 5" polyfoam support core with 5" of Talalay latex on top of that but the description you were given was a 6" + 4" design with Dunlop latex instead of Talalay.
I would want to clarify the construction and as I mentioned it’s unlikely that the Dunlop layer is in the 12 - 14 ILD range and I would ask about the density of the Dunlop as well.
Based on the type and quality of the materials it would certainly be worth considering as a possibility for one of your final choices depending on your confidence that it would be a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and all the other parts of your personal value equation that are important to you (including any exchange or return options that are available).
Phoenix