Hi kat888,
I can certainly help with “how” to make some of the choices you hope to make by providing information about the pros and cons of different options that are available to you but unfortunately there isn’t a formula that can predict how well any topper will work for a particular person on a particular mattress with any certainty because there are too many unknowns and variables involved to make specific topper suggestions and because softness/firmness can be so subjective and relative to different body types, sleeping positions, and individual perceptions as well as the firmness/softness of your mattress which will also affect how soft or firm your mattress/topper combination will feel as well.
The type of topper you choose would also be a preference issue because some people prefer the feel and response of different materials than others but there is more information about how to choose a topper in post #2 here and the topper guidelines it links to that can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success. It also includes a link to a list of some of the better online sources for toppers I’m aware of as well.
There is also more information about wool toppers in post #8 here and the posts it links to which also includes a link to a list of the better sources for wool toppers I’m aware of as well.
While it’s also not possible to quantify the sleeping temperature of a mattress or sleeping system for any particular person because there are so many variables involved with this as well and there is no standardized testing for temperature regulation with different combinations of materials … there is also more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range.
In many cases if you are sleeping warm on latex it can be from the type of mattress protector you are using or your sheets and bedding which can both have a significant effect on temperature regardless of the type of materials in a mattress or a topper.
Phoenix