Hi ddwaddle,
Post #2 here includes links to most of the more informative posts about mattresses and children in the forum which include links to some very good options for children.
Both of these are among the better options that mentioned in the children’s posts and would make good choices IMO. European Sleepworks sells Berkeley Ergonomics which has been mentioned many times in the forum and I think highly of the mattresses they make and the people behind them. (UPDATE: they are now making their own mattresses that use similar components in a similar range of designs). A forum search on Berkeley Ergonomics will bring up many posts about BE (including post #2 here which links to their children’s mattress but links to a different retailer).
The better options I’m aware of in the Greater Los Angeles area are listed in post #2 here. You have a lot of very good choices in the area that make or sell some very good quality and value mattresses.
Phoenix