Hi want2sleep,
The choice between Talalay and Dunlop is a preference choice and one isn’t any better than the other. Both of them are available in a range of firmness levels so either one would be fine in a suitable firmness. There is more about the difference between Dunlop and Talalay in post #7 here.
You may have read this already but just in case Post #2 here and the more detailed posts and information it links to have more information about safe, natural, organic, “chemical free”, and “green” mattresses and mattress materials that can help you 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” so you can decide on the types of materials or the type of latex you are most comfortable with having in your son’s mattress. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, and lifestyle choices. Latex can certainly be a good choice even for people that are very sensitive or for children.
The “safety” of any type of latex is also not something I would be concerned about and all the latex you are likely to encounter (Dunlop or Talalay made with either natural or synthetic rubber or a blend of both) will all have been certified by either Oeko-Tex or Eco-Institut for harmful substances and VOC’s (see post #2 here).
[quote]2. Is a single layer of 6" better, or is two 3" layers with mixed firmness better? We are looking at this site for this option. They only have Dunlop www.diynaturalbedding.com/ but good prices and nice ticking.
This is another option that would only come in 6" SleepOnLatex-latex-mattress-core[/quote]
This is also a preference choice and not a “better worse” choice. There is more about a single 6" core vs separate 3" layers in post #2 here. With a child it really wouldn’t make much difference either way since it’s unlikely you will need to fine tune the layering for a child.
Post #2 here and the posts it links to have more information about mattresses and children and there are some general guidelines for children in post #2 here. If you decide on a single 6" layer then I would probably choose something in the medium range and if you decide on two 3" layers than I would use a top layer of medium over either a medium or a firm layer underneath it. If your son is likely to be lighter than average then a slightly softer top layer (if you choose two 3" layers) would probably be fine as well since latex is more “supportive” than other types of foam materials. All of the suppliers you are considering will be able to give you good guidance about firmness choices for the latex they carry when you talk with them on the phone.
The glue they use would be water based rather than solvent based so most people would consider it to be very “safe” and I personally wouldn’t have any concerns with it but they will be able to provide you with more specifics about the glue they use than I would.
[quote]We hope to get ourselves a latex bed in the future. I love the DIY option.
We don’t have an unlimited budget, but want something safe and comfortable. Thanks! I have learned more than I ever though possible here! [/quote]
A component latex mattress certainly provides many options to “fine tune” the support or pressure relief of a mattress either by rearranging the layers or exchanging a layer but if you are considering going with a DIY mattress where you are buying the layers and the cover all separately rather than as a “mattress kit” then I would make sure that you have a good exchange policy on the layers just in case the choices you make don’t turn out was well as you hoped for (see post #2 here).
I’m glad the site was helpful to you 
Phoenix