Hi anmira75,
Post #2 here includes links to several posts with lots of information about mattresses and children which include some good quality and value natural choices. This recent thread and some of the links and references it contains may also be of interest to you.
Post #4 here includes the factory direct manufacturers or retailers that are closest to you and two of them have outlets that are within 10 miles of Waterloo, IA.
The Nook Pebble mattress has no information about what is in it but it looks like a polyfoam base layer and an inch of latex with a cover that includes polyester. This is certainly not organic and is also anything but natural and IMO it isn’t particularly good value either.
This is also a polyfoam/latex hybrid (similar to the Nook Pebble but uses higher quality and more costly materials and is a significantly lower price). They are a member of this site and I think very highly of them and the quality and value of the mattresses they make but they are also not a natural choice if that is important to you (polyfoam is not a natural material and is primarily a petrochemical foam although it is generally considered safe if it is made in the US or is CertiPur certified).
Hope this helps 
Phoenix