How can I extend my stay in Thailand with a tourist visa after holding an Ed Visa?

Yangon is possible and a good place to get a visa but it's not any quicker or easier to get to. You can fly from Bangkok, DMK relatively cheaply- Nok, Air Asia, Lion Air all fly there. You can get a bus either but it's a LONG way, you would really have to visit Myanmar to understand just how slow the buses and trains run there, I've taken 12 hours to cover 150km. IF a direct bus exists it's 24 hours at least from Bangkok. But flying to Yangon is also perfectly possible, it's just not fast. You can also do a land bounce into Myanmar and back from Kanchanaburi province if they haven't changed the rules, without getting a visa (only 30 days, and only 2 allowed per year).