Hi KG123,
With a latex mattress weight doesn’t matter because Talalay and Dunlop have different densities and each different firmness level of both also has a different density. This is very different from polyfoam or memory foam where the density of the material is independent of its softness/firmness level and is part of how you can tell their quality. With latex what you would need to look for is the type of latex (Dunlop or Talalay) and the blend of the latex (natural vs synthetic). Weight will also vary by the thickness of the latex layers and to a lesser degree by any differences in any other components as well such as the cover and quilting (although this will be a lower percentage of the overall weight).
You can read more about the different types of latex in post #6 here.
Jamison has made some changes to their lineup and don’t list the Comfort choice any more but as far as I know (and could find out online) the soft side had 2" of 19 ILD and 1" of 24 ILD in the comfort layer and I believe the 6" support core was 40 ILD. You can see it here but you could call them to confirm this.
Latex also keeps it’s firmness longer than other materials so it may have lasted longer than you thought although this would depend on many factors including your weight and the amount of softening that would still keep you inside your range for pressure relief and alignment.
this would depend on your sleeping positions, weight, and how much you were “going through” the softer 3" in the comfor layer but you would also be feeling the firmness of the latex support layer below this to some degree yes. Latex is the most durable of the foam materials but there are many factors to durability that are relative to each person (see post #2 here).
Phoenix