over 100 countries offer a visa waiver of 30 or 60 days, plus you can extend for another 30 for 1900 baht. you don't need to do anything other than the new tdac thing, which you should fill out online 3 days prior to your trip.
this is true, I did not know about the appointments and booked a flight to Vientiane, only to realize I could not get appt. Got appt in Savannakhet, and booked another flight from Vientiane to there.