Hi eeks,
You may have read this already but just in case you haven’t … post #2 here and the topics it links to has much more information about mattresses and children and choosing materials that are “safe enough” for children and includes a number of links to the better forum posts and topics about mattress and children as well.
The only reliable way to to assess the “safety” of different materials in more general terms is based on lab tests and the certifications they have for harmful substances and VOC’s so that you have some assurance than the VOC’s are below the testing limits for the certification (see post #2 here for more information about some of the more reliable “safety” certifications). If the materials in a mattress or the mattress itself has a reliable “safety” certification (which would be the case for almost all polyfoam that is made in North America) then for most people they would certainly be “safe enough”.
While it may be more information than you are looking for … there is a lot more information in post #2 here and the more detailed posts and information it links to about safe, natural, organic, “chemical free”, and “green” mattresses and mattress materials that can help sort through some of the marketing information and terminology that you will encounter in the industry and can help you differentiate between them and answer “how safe is safe enough for me” that can help each person decide on the types of materials they are most comfortable having in their mattress or on the certifications that may be important to them. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, beliefs, and lifestyle choices.
All the latex you are likely to encounter (either Dunlop or Talalay that is made with either natural or synthetic rubber or a blend of both) will have a reliable certification such as Oeko-Tex, Eco-Institut, or Greenguard Gold and based on actual testing I would consider any type or blend of latex to be a very “safe” material in terms of harmful substances and VOC’s. The polyfoam in their quilting and in the base layer is also CertiPUR-US certified so fo most people it would also be “safe enough”.
While it’s not possible to quantify the sleeping temperature of a mattress for any particular person with any real accuracy because there are so many variables involved including the type of mattress protector and the sheets and bedding that you use (which in many cases can have just as significant an effect on temperature as the type of foam in a mattress) and on where you are in the “oven to iceberg” range and because there is no standardized testing for temperature regulation with different combinations of materials … there is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range.
Latex is the most breathable and “temperature neutral” of all the foam materials (polyfoam, memory foam, and latex foam) so a mattress that has latex comfort layers wouldn’t tend to sleep hot for most people.
No, their mattresses are all inside industry standard dimensions and tolerances (see post #2 here) although it can sometimes take a few days for the mattress to completely regain it’s full size.
For younger children any mattress that uses materials that are “durable enough” that you would also consider to be “safe enough” and are in a medium to medium firm range would generally be a suitable choice for a child. The choice between different mattresses that meet these criteria would really be more of a budget and preference choice than a “better/worse” choice. 8" of latex is certainly more than you would need for a child (6" would be fine).
Latex comes in a wide range of firmness levels so the firmness of any latex mattress would depend on the firmness of the latex layers inside it. Even the firmest latex (that is generally used in the deeper layers rather than the top layers) has some give and wouldn’t be “rock hard”.
The effect of a quilting layer will depend on the specifics of the quilting and on the materials underneath it. Quilting can either firm up softer layers or soften up firmer layers. There is more information about quilted covers vs thinner more stretchy covers in post #12 here and the posts it links to.
All of the mattresses you are considering would certainly make a suitable choice for a child in a suitable firmness level.
Phoenix