Hi PhilOoster,
Post #2 here and the topics it links to have more information about mattresses and children and “safe” materials including a link to some general guidelines for children in post #2 here. It also includes a number of links to the better forum posts and topics about mattress and children as well which have more information about many good options for children which may also be worth considering.
There are some comments about the Naturepedic Organic Cotton Deluxe in post #2 here. It uses good quality, durable, and mostly natural materials that would be a suitable choice for a child … but of course not so much for an adult.
As you mentioned the Pure Echo uses a pocket coil and it would probably make a more suitable choice for most adults and it also uses high quality materials that don’t have any weak links in the design but of course the only way to know whether it would be suitable for any specific person would be based on your own personal testing.
It also uses a wool quilted cotton cover and wool is a great temperature regulator and since it’s also in a medium firm range it would also be a suitable choice for a child.
Phoenix