Hi Texasjoe,
There are far too many variables and it would take much more detailed conversations on the phone than I would possibly have the time for to design a mattress for someone else out of all the thousands of layering combinations that are theoretically possible. You can read more about why I don’t do this in post #2 here and post #2 here. My role is to connect the members here with the “experts” that do this every day and have a narrower range of specific options they have available rather than become the source of mattress designs for individual forum members. There is a great deal of information in the mattresses section of the site and on the forum (including in the posts I linked) that can provide more generic guidelines and give you some insights into a design that may be most appropriate for you but specific choices always need to be discussed with manufacturers or retailers that sell specific mattresses. My role is to help people find the “experts” that design and sell mattresses every day.
Latex can be “supportive” in all its versions. There are also two different types of support which I call “primary” support which is what “stops” the heavier areas from sinking in too far and is mainly about the deeper layers and also “secondary” support which is the support that helps to fill in all the gaps in the sleeping profile and provides lighter support for the more recessed curves of the spine or areas of the body. Latex also has a high compressions modulus or “support factor” which means that it gets firmer faster with deeper compression than other types of foam so even softer latex layers can be more “supportive” if you compress them to the point where they become firmer and “stop” your heavier areas from sinking in too much. “Too much” or “not enough” is relative to each person. The Puralux (and probably their base layer as well) is also Dunlop latex which has an even higher support factor than Talalay latex. It is also denser than soft Talalay at the same ILD.
Every layer of a mattress interacts with every other layer so the ILD of the top layer alone is only one of the many factors (layer thickness for example is just as important) that provides the support … or more accurately the spinal alignment of a mattress. The “goal” of support is is to make sure that your spine is in good alignment in all your sleeping positions and a mattress that is softer can provide just as good alignment as a firmer mattress depending on how evenly your body weight is distributed, which parts of your body tend to sink in more or less, and the relative surface area, shape, and mass of each part of your body. If you are sinking in evenly in all your sleeping positions then you would be in good alignment and then the overall softness or firmness would be more about how much you are “in” the mattress when your body comes to rest in each position and this would be a matter of personal preference rather than whether you are in good alignment. This would be a softer overall construction than would typically be used for your body type but this doesn’t mean that it won’t work for you. There are also many possible layering combinations that can produce good pressure relief and alignment along with the preferences for most people.
There are only 3 ways to “duplicate” a mattress that are discussed in the first part of post #2 here. Of these … the most likely would be if you were dealing with a manufacturer that had the same materials available in the same layer thicknesses and the same type of quilting and ticking. Other than this … different layers or materials would need to be 'translated" in terms of how close they may be overall to a layering or design that is different.
I would agree with “less noticeable than other materials” but it would still be noticeable IMO. Different people would have different perceptions about whether this was fine or if it was too much. I would definitely suggest trying the combination in person to see whether it would be acceptable to you. This concept would be similar to whether or not someone would feel a mattress that had a split layering (see post #2 here) but to a larger degree. It would depend on the tradeoffs that are most important to you … and possibly on how much you used the center of the mattress either for sleeping or other activities.
This thread mentions Denver Mattress in San Angelo, TX which up until a few days ago carried two mostly latex mattresses that may also act as a reference point if they still have any available.
Post #2 here also has some “possibilities” in the Midland/Odessa area but if may take a few calls to see if any of them carry any all latex mattresses.
Hope this helps … and one day I or someone else may develop a “formula” that will be able to provide specific suggestions for each person that is more accurate than personal testing or the knowledge and experience of a manufacturer that makes specific mattresses (and I know some that are working on it) but it has never been accomplished I doubt that this will happen any time soon 
Phoenix