@Elise ***********
you can't be self employed and working inside Thailand. If you mean you will be working remotely from Thailand then the DTV is really your only option but you can't work for any Thai entities or clients that are in Thailand. At your ages your options are limited visa wise for a stay of 1 year, even if you are not working the DTV is still probably your best option by signing up to one of the soft power activities with an approved provider (Muay Thai, Thai cooking or for medical treatment)