Can I extend a 60-day TR visa for an extra 30 days in Koh Samui, and what about the special tourist visa?

You can extend a 60-day Tourist Visa (TR) by an additional 30 days at your local immigration office in Koh Samui, and there is no need to go to Bangkok for this extension. Applications for the extension can be made before the initial 60 days expire. Additionally, the Special Tourist Visa (STV) is still available, but it must be obtained from your home country, allowing a maximum stay of 270 days that cannot be converted to another visa while in Thailand.