There are two main factors to consider when choosing a yoga mat, the first is the length of the mat which needs to be proportional to your size, and the second is the thickness of the mat. For many people, a standard size mat with a thickness of 5mm is suitable. If you're taller, you'll need a longer training mat, and if you feel you need more support, you might need to choose a thicker mat. Additionally, you should consider the material your mat is made of, and choose one that is comfortable for you as yoga mats come in a range of materials including vinyl, jute, and foam.