Hi rgvlubbdfw76,
Post #2 here has some links to the better forum threads and posts about mattresses and children and includes some good sources and ideas for children’s mattresses.
In terms of materials … I would strongly encourage you to avoid memory foam for younger children (there is more about this in the linked posts).
If you let me know your city or zip I’d be happy to let you know of any of the better options or possibilities I’m aware of in your area.
Phoenix