Hi Sark,
You may have read this already but post #2 here includes links to some of the better forum posts and topics about children and mattresses and they include much more information about some very good options and sources.
I would personally choose double sided in any of the versions they sell because of the extra durability and very reasonable extra cost. The choice of whether to choose latex or not would be a preference and budget issue and I would talk with them to help you decide between them. I would personally add the latex but that would only be my own personal preference and it would also depend on whether I could comfortably afford it … not because it’s necessarily a “better” choice.
I think it could also be a more suitable choice for parents that spend time with their children on their mattress when they are reading or snuggling because having a foam layer may be more comfortable for them as well.
If you are looking at local choices then the better options or possibilities in the New York City area I’m aware of are listed in post #2 here.
Phoenix