Hi iRFNA,
The guideline I generally use for lower density polyfoam (such as the reflex foam they use) in quilting layers is “around an inch or so or less” of lower density foams. They are quilted which compresses the foam and improves durability and they are thin and soft enough that any further softening will have a minimal effect on the overall performance of the mattress. Once quilting materials are 2" or more I would want to know the density of the quilting foam to make sure they aren’t a “weak link” but in thinner layers they are there for the “feel” of the layer and wouldn’t be a significant factor in the durability of the mattress.
That would depend on what materials were in the pillowtop or eurotop you were comparing it to. A pillowtop or eurotop mattress (or a tight top) is just a method of construction and can use any material or have any “feel” the manufacturer designs into the mattress (see post #2 here). They are generally softer because of additional layers of padding but a tight top can use the same thickness of padding materials as any other construction so it’s always the specifics of the mattress materials that makes the biggest difference.
Both latex and polyfoam are fast response materials but in general latex is more resilient (springy) than polyfoam. Memory foam is a slow response material that feels very different from both.
The softer and thicker the comfort layers are the more deeply you will sink into them regardless of which type of material is used.
Phoenix