Hi vita108,
As you can read here … I can only make meaningful suggestions about the quality and value of a mattress or help connect the members here to better retailers or manufacturers because there are too many variables and unknowns for me (or anyone) to suggest a specific mattress or design for any person. Your own careful and objective testing using the guidelines that are linked in post #1 here would be much more accurate than any “theory at a distance” I could offer.
Having said that I’m happy to make a few more generic comments.
in general terms … this would mean that you are looking for a firm enough support layer to “stop” your heavier pelvis from sinking down too far and “tilting” the pelvis which leads to changes in the curvature of the Lumbar spine and alignment issues. This is what I call primary support. You would also need to make sure that the upper comfort layers aren’t too thick and soft so the heavier parts of your body don’t “travel” too far before reaching the support layers which can also cause alignment issues and “push” your shoulders too far forward and created the “hunched” position you are referring to. Post #2 here may be worth reading as well. What all of this “translates to” is that your support layer needs to be 'firm enough" to “stop” your heavier hips/pelvis from sinking down too much in combination with comfort layers that are “just barely” thick and soft enough to relieve pressure points in your side sleeping position so that they have less risk in your other sleeping positions where pressure is less of an issue and support/alignment is even more important.
I don’t know the size you are looking at or what goes with the mattress (foundation etc) but Electropedic are among the better value choices in the Los Angeles area and they are certainly much better value than the mainstream brands that most people end up purchasing.
With Talalay latex … density information is not important because the ILD’s are usually accurate. Density is more important with Dunlop not because it makes a difference with quality but because it can often provide more accurate comfort information than ILD which is often incorrect with Dunlop. If you are testing a mattress in person … then neither density or ILD with latex is important because both of them are “comfort specs” and careful and objective testing is much more meaningful than knowing the actual softness or firmness of a layer. With latex it’s the type and blend of the latex that is important to know (which they have provided). With polyfoam and memory foam then density information is important to know because it indicates quality although even here ILD or “comfort information” such as IFD (roughly equivalent to ILD) is not important when you are testing a mattress in person.
I should clarify as well that both Radium and Latex International are currently using a 30/70 blend.
You can read a little more about the differences between 100% natural Talalay and blended Talalay in post #2 here. they are very similar in their “feel” although if someone was testing two mattresses where the whole mattress was one type and the other was another type of Talalay then the differences may be more noticeable for some people than two mattresses where only a single layer was different (assuming that both use the same thickness and ILD each type of talalay in every layer and that the cover/quilting material was the same as well) because natural Talalay is denser than the blend (it will get firmer a little faster) and natural latex is more elastic than synthetic latex.
Again I would make the same comments as above. “Feel” is also very subjective and the differences between different versions of Talalay would be much smaller than the differences between Talalay and Dunlop. They are similar enough that there would be no way to know or predict if any specific person would feel the differences in different constructions unless they actually tested two mattresses that were otherwise identical in a side by side test. Even if two mattresses use exactly the same materials but have differences in design (such as layer thickness) they may feel different for some people but possibly not others (if the differences were smaller) if they are compared side by side.
Again … only your own personal testing or sleeping experience can really know any differences you would feel when you are dealing with relatively small differences in design and materials.
If they were the same material then probably not no. This would be especially the case if the two separate layers were laminated together. Separate layers will “act” softer in theory but I doubt that this would translate into an actual perceptual difference for most people.
When I talked with them in 2011 they told me that they were having “supply issues” with latex and didn’t have any and then when I talked with them last September they said they had the latex hybrids listed on their site on their floor. I just called them again and they are once again saying they have “supply issues” which seems very odd to me because latex of all different types is widely available to manufacturers. Regardless of the real reason though … thanks for the heads up and I’ve changed the listing to reflect that the latex hybrids that are listed on their site are not available 
Phoenix