will be in yasothon later this year, will be looking to get to chang mai, is there a decent quality bus available ?

If you are in Northern Yasothon ,you could try Going to Khon Kaen to get to Chiang Mai. I don't personally know about this way to go .If ,you are in Southern Yasothon, then definitely you can catch Nakhon Chai Air, ChianG Mai service ( do have excellent VIP, but they call it First class) from either Surin or Si Sa Ket. Dependent on which is closer for you. It picks up in both cities, for Chiang Mai. N.C.A. is most probably the best bus line in Thailand.

I don't know about this route but I've used NCA between Bangkok and Khon Kaen and it's the best I've seen. They also seem to take safety seriously and change drivers.