If you have a 30 day tourist visa that has never been extended before, it should hold true that you can get another 30 days from immigration without a letter from your embassy. Right?
Asking for a friend. Thanks.
TLDR : Answer Summary
Yes, you can extend a 30-day tourist visa without a letter from your embassy. You can obtain an additional 30 days at your local immigration office for a fee of 1,900THB, provided that the visa has never been extended before.