A Wave can cover long distances, especially the 125 Wave, and comfort is a personal thing .... personally I find the Wave reasonably comfortable and my knees are not constantly hitting the plastics, as with a Click, Scoopy etc.
But .... you'd need to be happy travelling in the left lane and frontage roads with all the other small bikes, busses, 'rot puang' sidecars and tractors. Riding like that gets old pretty quickly.
A bit more power will allow you to keep up with traffic, get to the front of the pack at the traffic light drag race and find those quieter sections of road out of the gutter.
A 160 PCX, ADV or 155 Yamaha is a little better, but a 350cc Honda or Yamaha 'super scooter' is a lot better.
My personal choice is the Kawasaki Versys X300 .... quick enough for longer distances in Thailand. The Honda CRF 300 is just as good, and 500 twin is even better.
But if ypu take it slow, and have the patience, any bike can do long distances.