Hi Nemix,
I’m not so certain that you are in the best position to be providing this type of guidance to someone else since you are only beginning your own learning curve about choosing a mattress and a topper and I certainly wouldn’t agree with your comments here.
The most important part of the value of any mattress/topper purchase would be how well you sleep on it followed by the quality and durability of the materials followed by all the other parts of each person’s personal value equation that are important to them and there are too many variables involved for anyone to be able to predict this with any certainty.
The thickness of a mattress or any individual layers or materials inside it is really just a side effect of the design and the design goals of the sleeping system and is also only one of many variables that can affect the feel and performance of a mattress/topper combination relative to any specific person and by itself isn’t particularly meaningful (see post #2 here).
Phoenix