For beginners, the suggestion is to buy a thicker yoga mat, preferably about 6-8 mm. If it is too thick, it will easily lead to ankle sprain during practice.
After gradually mastering the essentials, you can change the yoga mat from 3.5 mm to 5 mm; General professional yoga practitioners will choose the thickness of1.5-4 mm.
Of course, don't try to be brave, and buy professional yoga mats in order to give people a professional feeling, which is not conducive to your own practice. Just like buying clothes, what suits you is the best.