Bangkok Airways, one flight a day non-stop, about £100 including tax, will stop massive amounts of faffing about!

Thanks for that advice, just wondering now whether it is best to book the flight in advance but not sure which day we want to leave Chaing Mai, would prefer to have a bit of flexibility with our timetable. Is it easy and cheap enough to book a flight to Koi Samui when we get to Chaing Mai or should we really do it in advance?

I have known Bangkok airways flights get pretty full...up to the point where I could not get off Samui to Bangkok to connect to my international flight back as I had left confirming my flight too late - had to do a quick reroute via U Tapao. Not sure how busy the flight gets from Chaing-Mai to Samui - might be worth contacting Bangkok Airways for advice...I've always found them helpful.

Yeh - as Sunbear says, the flights can get full (come November you won't get a Bangkok - Samui flight for Christmas / New Year despite their being about 40 flights a day!). May should be pretty quiet, however, the Far East has a habit of springing unexpected national holidays on you when you least expect it (for example - Golden Week in May - a Japanese holiday leading to many Balinese hotels being completely full!), so if you want that flight, then book ahead and work around it.

However, if you are flexible enough to be able to travel by other means (connecting flights, train etc) you should be OK to do it when there. Probably!