Hi railit,
I’m glad you’re still enjoying your mattress.
Only your own personal testing of the product will be able to answer that question for you. If you want to learn about the relationship between surface plushness and support, there is 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”.
While photos can be helpful in comparing how you look when using one configuration versus another, unless you are able to document key landmarks on your body (like in biomechanical analysis) and subsequently analyze this, it would be difficult to tell froma photo if your alignment is truly “off” unless there was an obvious deviation. You’re actually performing the best way to analyze this by trying out the product in person. If you notice more pain in the morning in your lumbar region and it takes longer for it to go away during the day, this may be an indication that there is too much surface plushness with this additional topper. There is more about diagnosing the most common symptoms (types of discomfort/ pain) that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here, just in case you start to experience some pains with this new combination .
There are many forum members who use 4" or more of plush latex on top of their mattresses, but I wouldn’t use their results or comments as any sort of a reliable guideline as to what might work for you, because this is too subjective and relative to different body types, sleeping positions, and individual preferences, sensitivities, and circumstances and you are the only one that can feel what you feel on a mattress.
Personally, I would use the topper for the entire two-week period and see how you adjust during that time frame and then make up your mind after that time if you wish to seek a firmer level of surface comfort.
I’ll be interested in learning about what you decide to do.
Phoenix