Hi B4Bob,
I’m not Beekeeper of course so they will hopefully see your post and reply to your questions more specifically but I can make some general comments about firmness choices.
There are no “standardized” definitions or consensus of opinions for firmness ratings and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. 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 (or vice versa) 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 very subjective 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).
In very general terms firmer materials will tend to feel softer to someone that is in a higher weight range than the same materials would feel for someone that is in a lighter weight range because the materials compress more easily with greater weight and pressure. Heavier body types will also tend to need firmer materials to prevent the heavier parts of the body from sinking in too much to provide good alignment as well. Sleeping positions can also make a difference in the firmness choice that is best for each individual person. If a mattress is too soft to provide good support/alignment for the person sleeping on it in all their sleeping positions then there would be a higher risk of alignment issues and the lower back pain or discomfort that can go with it.
This is also why I would also be very cautious about using other people’s experiences or reviews on a mattress (either positive or negative) as a reliable source of information or guidance about how you will feel on the same mattress or how suitable it may be for you and in many cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person may be completely unsuitable for someone else to sleep on (see post #13 here).
Phoenix