Hi Del,
This normally wouldn’t be an issue with a good quality tight fitting cover but you can see some of the pros and cons of a component mattress vs a “finished” mattress with a tape edged cover and glued layers in post #15 here.
There is more information about polyfoam comfort layers in this article and about polyfoam support layers in this article. Polyfoam is the most common foam material used in the industry and it’s the material that you will most commonly find in the comfort layers of most innerspring mattresses (although they are generally lower quality and less durable versions of polyfoam than the 12 in 1 customizable mattress is using) and is the material that you will also find in most sofas as well. It is generally a lower cost foam compared to specialty foams like memory foam or latex although it comes in a wide rage of firmness levels and foam densities that are more or less durable and have a wide range of different properties.
There is more about latex comfort layers here and latex support layers here and there is more about the pros and cons of latex in this article. There is also more about the different types and blends of latex in post #6 here.
There is more about memory foam comfort layers here but you won’t find memory foam in the deeper support layers because it doesn’t come in versions that would be firm enough. There is also more about the pros and cons of memory foam in this article and more about the many different types of memory foam in post #9 here and in post #8 here.
There is also a comparison between the pros and cons of latex vs memory foam in post #2 here (polyfoam would be closer to latex in terms of “feel” because it’s also a fast response material).
Post #4 here also includes the foam quality guidelines I would suggest (along with the post about higher weight ranges I linked in an earlier reply).
The best way to know for certain which types of materials or mattresses you tend to prefer or that would at least be “acceptable” to you in terms of their general “feel” would be based on your own personal testing or sleeping experience.
Phoenix