Hi Treadinwell,
If the foam is low quality/density then more is worse.
If the foam is a good quality/density material then the “right” amount is the “best” amount. Too much or too little for you can both lead to a mattress that is unsuitable for you. All the layers and components of a mattress interact together and if you do some careful and objective testing on a mattress and the mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) then the amount of foam in it is “right” … for you.
Any “strategy” or mattress design can work well for some people … and be completely unsuitable for others. I would avoid trying to “design” your own mattress ahead of time and focus on what your mattress testing and your body tells you and then if a mattress is a good match for you then all you have to do is make sure that it uses good quality and durable materials so that it won’t soften or break down too quickly relative to the price you paid. Post #13 here has more about the most important parts of the “value” of a mattress purchase.
If you can test a mattress/topper combination in person then it can be just as good a choice as any other sleeping system that works well for you. If you can’t test a mattress/topper combination in person then I would avoid this approach unless there are no better alternatives or if in spite of your best efforts you end up purchasing a mattress that is too firm for you because without testing the combination in person it can be almost as difficult to choose a suitable topper that works well for you with a specific mattress as choosing a mattress in the first place (the specifics of the mattress will make a significant difference in what topper will work best for you).
If you follow the steps in the tutorial post one at a time you will have the best chance of making a successful mattress purchase.
Phoenix