Hi janello,
All of the options you’ve mentioned certainly use good quality materials although they use different types of latex (you can read more about the different types of latex in post #6 here and in post #6 here).
You’re certainly in the range I would use. I would use a minimum of 28 but 32 is probably better as a minimum.
The prescription is so that they can legally make it without a fire retardant and it will also save you in taxes.
No … they use the wool as the fire barrier to pass the fire code. You can read more about fire retardants in post #2 here and in post #4 here. This mattress uses blended talalay latex (which like 100% natural Talalay latex is Oeko-Tex certified) but you can also upgrade this to 100% natural Talalay as well.
This is one of the few mattresses in the US where the mattress itself is certified organic (rather than just the materials inside the mattress). Of course an organic certification doesn’t necessarily mean the mattress is any “safer” than a mattress that uses materials that are just as “pure” but not certified as organic. Compressed cotton will be very firm and if you spend any time on the mattress may be too firm for an adult. Naturepedic is also good quality but not particularly good value. If I was looking at a natural fiber/innerspring mattress for a child I would probably consider this one which is made by one of the members here and uses wool which is more resilient than cotton. It still won’t be as resilient or soft as latex though and will also become firmer as the wool compresses (although not to the same degree as cotton).
The question of “how safe is safe enough for me?” is incredibly complex and has no easy answers. In most cases the answer will vary with the priorities and beliefs of each person. Post #2 here has more about this but in general I would consider latex, natural fibers (either without any chemicals added or certified organic) and innersprings as the most “natural” or “safe” materials for those whose definition of “safe” is more stringent than the norm.
Phoenix