Hi toorhax,
Their Oeko-Tex certification may be under a different name but if their Oeko-Tex certification is still valid they should be able to provide you with their certificate number that you can confirm on the Oeko-Tex site if you call or email them and ask.
I think that a “healthy” mattress is somewhat of a misnomer. A mattress needs to provide for healthy sleeping which is mostly a function of PPP (Posture and alignment, Pressure relief, and Personal preferences) and the materials need to be “safe” from toxins and offgassing but healthy sleeping is more about the performance and function of the mattress and safety is more about the chemical composition or type of materials in the mattress and they are really two separate issues. A mattress can use “safe” materials and still not be the best design for healthy sleeping for your specific body type, sleeping style, and individual circumstances. There is more about “healthy” sleeping in post #4 here.
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 (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 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.
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 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” and that can help you decide on the type of materials and components you are most comfortable having in your mattress or on the certifications that may be important to you. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, beliefs, and lifestyle choices.
Phoenix