Hi Skyrial,
There is more about the different ways that one mattress can “match” or “approximate” another one in post #9 here but these are completely different types of mattresses and would be difficult to compare because the materials they use are so different (one is latex and the other is polyfoam) and these types of comparisons can be very subjective and relative to the perceptions of each person.
There is also no “standard” definition or consensus of opinion for firmness ratings and different manufacturers can rate their mattresses very differently than others. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress that is firm for one can feel like “medium” for someone else or even “soft” for someone else depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. This is all relative and is as much an art as a science. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see post #15 here).
The best place to start your research for a new mattress is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and know how and why to avoid the worst ones.
If you are looking at an online purchase then the tutorial includes a couple of links to two lists of some of the better online options that I’m aware of (in the optional online step).
There is also more about the pros and cons of some of the newer “breed” of “one choice fits all” mattresses such as Tuft & Needle in post #3 here.
If you are interested in more local options that you can test for firmness in person before a purchase then the better options or possibilities I’m aware of in the Seattle area (subject to the “value” guidelines here) are listed in post #2 here.
Phoenix