Hi 10sChick,
I’m glad to see that your very “creative” solution worked for you and I hope it continues to work over time as well.
Your solution includes two main factors that are working well together. The first is that a topper can reduce or at least slow down the amount of heat that reaches the memory foam which can “firm up” memory foam or at least slow down how quickly it becomes softer over the course of the night (depending on the specifics and temperature sensitivity of the memory foam). Posts #5 and #6 here are another example where this helped as well. The second is a zoning scheme that can also help with alignment issues by adding firmness under the parts of the body that need it without affecting the firmness under the parts that need to sink in more deeply.
For the sake of others that may read this … I would keep in mind that what works for one person may not work nearly as well for another and it may not continue to work as well once the foams in your mattress begin to soften over time but regardless of any of that or how long it will continue to work for you … it’s working for you for now which is all that matters and it may also be helpful for others that are in a similar situation as well.
Part of your solution is similar to some of the suggestions in post #11 here about zoning and I’m impressed that you had either the intuition or the knowledge to try it 
Thanks again for sharing your suggestions!
Phoenix