Hi rupert,
This is unfortunately very true … especially if you are dealing with major brands or most of the mass market retailers or chain stores. They don’t really care about the quality of what they sell and their sales are based on “showroom feel” which of course won’t last long if the materials inside are low quality.
The firmness of a layer depends on the ILD of the latex whether it’s in a pillowtop or a tight top. How soft or firm it feels will also be modified by the layers that are above or below it. While a pillowtop can use any type of foam … this type of construction provides more independent movement at the edges (the edges are not directly attached to the mattress) so a pillowtop can feel a little softer than if the same layer was inside the mattress itself. I would make sure that any pillowtop didn’t contain more than an inch or so of lower quality foam but if the pillowtop uses high quality foam in it then it would be fine. You will also find foam used in a quilting layer with or without a pillowtop (this is not usually latex) and in this case the quilting can make the foam firmer and the tighter the quilting pattern the firmer the quilted foam will feel.
some of the better options and possibilities in the nashville area i’m aware of are in post #7 here.
Phoenix