Hi Brick,
ILD’s specs are not very meaningful when you are testing a mattress in person because each person can have a very different needs and a much different sense of what is soft, medium, or firm based on their body types, sleeping positions, and sensitivity. Your body and careful testing will tell you much more than ILD when it comes to deciding on which mattress best meets your needs and preferences than any ILD specs.
Some guidelines for testing for pressure relief are in this article and for support and alignment are in this article and in post #11 here.
The specs that are important when you are looking at local mattresses are “quality specs” and “value secs” which are the thickness of each layer and the type and quality of the materials (rather than their firmness or softness). In the case of the mattress you are looking at … Dunlop latex is a high quality material and the overall value of the mattress would depend on the cost of similar mattresses (with 9" of the same type of latex and similar ticking/quilting) compared to the one you are looking at.
A “medium” Dunlop base with a 3" soft Dunlop topper would be a very popular choice for people of your height and weight who liked the feel of Dunlop in all the layers of their mattress.
Dunlop latex (or any latex for that matter) doesn’t come in exact ILD’s and there is a range of ILD’s across the surface of the layer. You can read more about ILD’s in post #6 here.
As a reference (and bearing in mind that the layer you are trying won’t be exactly this) … 28 is usually considered to be medium and 32 would be medium firm (and some would call this medium as well) but each person would have their own rating and idea of how it feels to them.
Support is really about how well a mattress keeps your spine and joints in a neutral alignment and if you are in good alignment on a mattress in all your sleeping positions then for you the mattress has good support (even though for someone else it may not). Dunlop latex that was “in the range” of 32 ILD would be suitable for many people as a support layer but it would also depend on other factors such as the thickness, firmness, and type of materials that were on top of it. Your own testing results are always more important than any “theory at a distance” when it comes to how well a mattress works for you.
I think this can be a very good option if it’s necessary (and again theory is not as important as your own personal results when it comes to deciding if it is necessary). Sometimes it can even be surprising that a mattress that is layered the same on both sides can be suitable for two very different people (see post #2 here). Some of the pros and cons of split layering are in post #2 here.
With a split layer mattress … I would make sure that the sides weren’t glued together (at least until you knew for certain that it was what you wanted) or you would lose the benefit of being able to change one half or the other. It’s not likely that you would feel a seam if there was a layer of latex on top or even if the mattress used a quilted cover without a solid layer over a split (although you would feel the difference on each side of course which is the reason for the split).
Hope this helps.
Phoenix