Hi ninatulia,
Welcome to the Mattress Forum! 
Just for a reference, I’ll copy here some of the information from my previous posts below in this thread, as having a mattress certified as “organic” (GOTS or GOLS) is not a safety certification.
The only reliable way 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 VOCs so that you have some assurance than the VOCs are below the testing limits for the certification. If the materials in a mattress or the mattress itself has a reliable “safety” certification, then for most people they would certainly be “safe enough” … regardless of the type of material or the name of the manufacturer on the label.
I would also keep in mind that most people that are looking for an “organic” mattress or materials are usually more concerned with “safety” than whether the materials have an actual organic certification and in many cases are confusing an organic certification with a safety certification. There is more information about the three different levels of organic certifications in post #2 here and some of the benefits of an organic certification in post #3 here and there is more about the different types of organic and safety certifications such as Oeko-tex, Eco-Institut, Greenguard Gold, C2C, and CertiPUR-US in post #2 here and more about some of the differences between organic and safety certifications in post #2 here and there are also some comments in post #42 here that can help you decide whether an organic certification is important to you for environmental, social, or personal reasons or whether a “safety” certification is enough.
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 (which are the same safety certifications that you will find for certified organic latex) or C2C (which has only been passed by Radium which makes Talalay latex) and based on actual testing I would consider any type or blend of latex (regardless of whether it is natural or synthetic or a blend of both) to be a very “safe” material in terms of harmful substances and VOC’s (offgassing). If the safety of a mattress is what is most important to you then a GOLS organic certification for the latex wouldn’t be relevant because it’s not a safety certification and you would also be able to consider Talalay as well as Dunlop.
Regarding making a mattress based upon your specifications, you’d have to find a manufacturer first that was already producing a product using the materials you personally feel are safe, and then you’d have to see if they can create that product to the specifications that you desire, which might involve a note form a health care professional (see post #4 here and post #6 here ). Without knowing what actual materials you desire to use, I unfortunately can’t provide any meaningful suggestions.
Phoenix