Hi lcs101,
You are wise to be concerned about the materials used to provide edge support and their longer term durability. You can read a bit more about edge support in post #33 here and post #2 here. There aren’t a lot of memory foam mattresses that have edge support because for most people it’s not necessary and it can be a way for a manufacturer to reduce the cost of higher quality materials in many cases but for those where this is a desirable option there are a couple of examples of a better design in the first post I linked. The key with edge support for those that plan to use it either for sleeping or for sitting is that it is made of a very durable material that doesn’t soften sooner than the other foam in the mattress or remain so firm that when the foam you sleep on softens you end up sleeping in a well.
Some of the better options I’m aware of in the Nashville area are in post #7 here but I don’t know which if any of them carry memory foam mattresses that have edge support so you would need to call them and ask if this was in important factor in your choice.
Phoenix