@Dianne *********
With a South African Passport (if that’s your origin), you can enter on a 60 days visa exemption and apply for a Non O inside Thailand. You’ll probably need a visa agency to assist you as you’ll not be able to open a bank account without a long stay visa.
Otherwise If the actual embassy/consulate accept foreigners to apply it normally should be quite straightforward to apply for a Non O as long as you fulfill formal qualification and can prove a bank account with the required funds.
Several people have applied for a Non O e-visa without issues through the consulate in Ho Chi Minh City or the embassy in Phnom Penh as an example.