Hi kercove,
While I can’t help with what to choose because each parent can have very different criteria … I can certainly provide more information that can help with how to choose.
Post #2 here includes links to the better forum posts and topics about children and mattresses and they include more information and links to many good choices for children’s mattresses as well.
There is also more information in post #2 here about the “safety” of different types of mattress materials that can help you with the first step which is to decide on which materials you are most comfortable using in your son’s mattress. The only material I would avoid completely with children’s mattresses would be memory foam but other than that it would be a matter of budget and personal preferences.
Naturepedic certainly make some high quality mattresses that would be suitable choices but they are also in a higher budget range than many other similar options that are available to you. I also think highly of Gardner Mattress (see the end of post #13 here) and they would be well worth considering and are included in the list of the better options and possibilities I’m aware of in your area in post #2 here as well.
Phoenix