Hi Orchid,
Just like with mattresses … there are too many variables and preferences involved to use a “formula” to choose a topper with any degree of accuracy. While I can certainly vouch for the quality of the toppers that are sold by Rocky Mountain … I would have no way of knowing how it would feel for you without a frame of reference of similar topper / mattress combinations you have tried.
The most accurate way would be to test a specific topper/mattress combination in person but of course this isn’t possible so the next best way would be to test a similar topper on top of a mattress that was similar to yours so you would have an idea of how the combination would feel and perform for you. Even testing mattresses with 3" or 4" of latex on top where you knew the softness of the latex would be very helpful to give you a sense of how your mattress and a topper would feel for you but you may have to do some calling around in your area to find a mattress that would approximate what you are considering. If you let me know your city or zip I’d be happy to let you know of any possibilities for retailers or manufacturers in your area I’m aware of.
If that isn’t possible either … then post #2 here and the posts it links to have some guidelines for toppers that can increase your odds of making the most suitable choice.
Your topper will interact with the comfort layer that is already part of your mattress and based on the description here (which is not that detailed) … your mattress has an inch of latex (of unknown firmness) over a 6" polyfoam base (of unknown density and unknown firmness). If your mattress is about 7" - 8" thick then these would probably be all the layers. If it’s thicker then there are layers missing in the description. If you only have a 1" comfort layer then I can certainly understand that you would need some extra softness and pressure relief because this is thinner than the norm for a comfort layer and it could certainly use some “help” for side sleepers in yur weight range in terms of pressure relief.
Phoenix