Hi NewToLatexInFL.
I am guessing that you came across my comments in this post #6 here where we discuss a mattress/topper combo using a 2" or 3" PTB topper.
What the salesperson recommends is what I call a dominating layer arrangement, which will have a crisper and on the mattress feel which may or may not be achieving the “extra cradling” effect that your wife loves. A mattress is always a balancing act between the need to “allow” the lighter parts of the body (such as the shoulders and upper body) to sink in enough into the upper layers (for pressure relief) and “stop” the heavier parts of the body (primarily the hips/pelvis) from sinking down too far into the deeper layers so that your spine is in good alignment.
Generally speaking, when you use a topper over a mattress two things will happen. The first is it will compress and in combination with the layers below it will take on the shape of your body profile. Softer toppers will compress more than firmer toppers. This “cradle” formed by the upper layers re-distributes weight away from the pressure points of the body. The second is it will “bend” into any softer foam below it. This “bending” will happen more if the topper is firmer than the layers below it (what I call a dominating layer) because the lower layers will compress more than the upper layers and the topper will “bend” into the compression (or even any dips or soft spots) of the foam below it. This means that the surface of the mattress will be slightly less conforming and feel firmer (less pressure relieving) and you will have a more “on the mattress” feel than if you were sinking into a softer topper even though the next layer down is still compressing. Many people who are taller and slimmer will prefer a firmer feel like this because they are often be “sprawlers” and prefer a more on the mattress feel with more freedom of movement.
The downside to this arrangement is that the recessed gaps are filled in a little bit less than if the topper was softer and the lighter parts of the body (such as the shoulders) may not sink in as effectively for both upper body alignment and pressure relief. This being said I’d suggest that you and your wife try this arrangement in the shop and see how it works out for you.
I look forward to hearing about the results of your week’s testing.
Phoenix