Hi marina_v,
Oeko-Tex is a safety certification that involves testing a material for harmful substances and VOC’s to make sure that the amounts are lower than than the testing criteria and GOTS is an organic certification that is used to certify that a product was made using certified organic raw materials and manufacturing processes and doesn’t test for “safety”. There is more detailed information about safety and organic certifications in post #2 here and the posts it links to and in post #2 here.
Phoenix