Hi, perhaps it's a bit late to answer your question but maybe my answer can help people with the same problem.
There are very thick yoga mats available on sites like Aliexpress for a very good price.
You should not only search thickness in a mat but density so it helps your balance and does not feel like a mattress.
Also grip and many other traits that are better explained in articles like this one about how cheap yoga mats end up being expensive in a short time and tips on how to choose a quality one.