Hi Maverick76er,
While I can certainly help with “how” to choose, it’s unfortunately not possible to make specific suggestions or recommendations for a combination of toppers for you because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person, and there’s nothing that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
Regarding adding toppers, there is quite a bit of good information about selecting a topper and links for some of the better topper sources of which I am aware in post #2 here. There is also a list of sometoppers that can be returned here.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel” that may be useful as well.
Of the three scenarios you listed, the best option would be placing latex between your topper and the mattress. You said you desired the feel of memory foam, so placing latex on top would negate that. Adding more memory foam would allow for more sinking in, which you are complaining about. Adding latex in between the topper and mattress will provide for a bit more comfort, but won’t sink in as much as using a second topper of memory foam.
Phoenix