Hi petrina french,
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 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.
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, Greenguard Gold or C2C 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) to be a very “safe” material in terms of harmful substances and VOC’s (offgassing).
Most people that are looking for an “organic” mattress or materials are usually concerned more with “safety” than whether the materials have an actual organic 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.
The choice between different types and blends of latex is also more of a preference and budget choice rather than a “better/worse” choice and any type or blend of latex is a durable material relative to other types of foam materials. There is more about the different types and blends of latex in post #6 here and more about how Dunlop compares to Talalay in general in post #7 here but the best way to know which type or blend of latex you tend to prefer will be based on your own testing and/or your own personal experience.
Phoenix