Hi lamaufder,
You’re welcome. 
When you have so many specific questions, I always recommend a phone conversation directly with the manufacturer. You’ll get the most prompt, detailed and personalized information in that manner.
There is no one standard rating of firmness across styles of beds, or generalizations of one style versus another. Latex and memory foam are two entirely different styles of foams with different properties, and there are differences in the properties of each type of foam (ILD, response rates, compression modulus…), variances in thickness that can change feel, and then there are the other materials contained within the remainder of the mattress that will also have an impact on comfort. SO while the question seems simple on the surface, it’s actually a quite complication interaction of many variables that ultimately determine the overall feel of a mattress.
Latex and memory foam in the upper layers of the mattress tend to be two very good products at pressure point relief. Of course, they are part of a complete mattress system so they work in conjunction with the rest of the mattress componentry.
Latex and memory foam are very different materials with very different properties and both of them come in a wide range of different versions that each have differences in their properties and a different “feel” or firmness level but the choice between them is more of a preference and budget choice than a “better/worse” choice. There is more about some of the general differences between memory foam and latex in post #2 here. Some people tend to prefer the faster response and more resilient and “on the mattress” feel of latex and some prefer the slower response and more “in the mattress” feel of memory foam and some people may prefer some combination of both of them but the only way to know which one you tend to prefer in general terms will be based on your own careful testing in a store or your own personal experience when you sleep on them.
The overall firmness (surface comfort) of a mattress isn’t something that’s necessarily specific to individual latex brands, but by the combinations and styles of latex layers used to create your own mattress.
The ILD of the latex isn’t particularly meaningful as it relates to the quality of the foam, and many brands consider this information proprietary, so it’s common for that information to not be listed on a company’s web site. However, with a phone call a knowledgeable representative could certainly relate the softness of different components within their lineup and help you to understand how one layer might compare to another that you may have tried, and how those layers can perform in combination with each other.
While knowing the specs that can affect the quality and durability of the layers and components in a mattress is always important … unless you have a great deal of knowledge and experience with different types of mattress materials and components and their specs and different layering combinations and mattress designs and how they combine together and can translate them into your own “real life” experience that can be unique to you (which would generally be a very small percentage of people) … I would tend to avoid using complex specifications to try and predict how a mattress will feel or perform for you. When you try and choose a mattress based on complex combinations of specs that you may not fully understand or only based on specs for single layers or components that may not be as relevant or meaningful as you believe it is then the most common outcome is “information overload” and “paralysis by analysis”. Even the best mattress designers in the industry are often surprised at what a mattress they design “should have felt like” based on the specs when they design it and what it “actually feels like” when they test out their new design. My best advice is to relate to an experienced manufacturer you current layerings, your current state of comfort, and what you’re attempting to achieve, and then rely upon their expertise to make suggestions that will hopefully lead you in the proper direction.
This is certainly a concern with any mattress combination you choose. The ideal would be to have both suitable support/alignment and comfort/pressure relief in a mattress, but if you have to choose one over the other then I would choose support/alignment. There is some great information in this PHD thesis by Vincent+Verhaer (who is one of a group of researchers that I greatly respect) about the importance of good spinal alignment that clearly indicates that for healthy individuals it has the single biggest effect on the depth and quality of sleep and recovery for healthy individuals. Having proper alignment doesn’t necessarily mean that a mattress needs to feel hard like a board, and in your situation you certainly would want some plush surface comfort along with this deep support.
Not to overload you, but if you want to learn a little about pressure relief and support, there is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”.
How your mattress falls within the “overall spectrum in firmness” isn’t something I’d tell you to pursue because such a spectrum doesn’t exist (there is no absolute comfort scale) and even if such a scale existed you should instead focus upon your current level of comfort and then relate that information in a phone call to Flexus and describe to them what you’re trying to achieve and the combination you’re thinking of keeping, and they will in turn relate to you if they’re able to achieve what you’re trying to describe, and they’ll be most knowledgeable to recommend if that combination will provide adequate support for you.
Phoenix