Hi LikeToHike,
This would depend on the type and condition of the boxspring you have. Different boxsprings can certainly change how a mattress feels and performs. There’s more about this in post #2 here.
Yes … your thinking is on track. If a mattress is too soft and doesn’t provide proper support and alignment … it’s very difficult to “fix” because any firmer materials you put on top will tend to still “bend into” the softer materials below so the effect would only be limited. On the other hand … if a mattress is too firm … it’s much easier to “fix” the pressure relief by adding a softer layer on top and as long as the layer is “just enough” … then support and alignment won’t be compromised.
There is also one outlet in San Angelo that may be worth visiting as a point of reference if nothing else. They are …
Furniture Row® Store Locations - Store Hours & Addresses They are a regional factory direct manufacturer that makes a range of mattresses with better quality and value. They also make two “mostly latex” mattresses (the Aspen and the Snowmass) which would give you a sense of how latex feels and can act as a reference point for testing. The 2" latex layer they use on top of both (and both also include an inch of polyfoam in the comfort or quilting layers) is 24 ILD.
Phoenix