Your best option of an automatic scooter available today in Thailand for comfortable riding over longer distances is the Honda SH150i.
With it's 16” wheels it is very comfortable for long commuting, but still very easy to riding in busy traffic. The 150cc PGM-FI powered engine is both powerful enough to give you a smooth ride, at a good speed and still very fuel economic.
As alternative I would recommend the Honda Wave 125i, which is a semi-automatic (4-speed without clutch), which has 17” wheels and is the work horse of Thai motorcycling and probably the best bike to ride in Thailand without paying a lot of money. The Honda Wave 125i is also equipped with the Honda PGM-FI (fuel-injection) system…. And is with its four-speed transmission even more fuel efficient. Shifting gears on the Honda Wave 125i is extremely easy, to change gear you turn the throttle back shift up and open the throttle again….
How long distance is long distance? What types of roads? I used to commute 20-ish kms and could travel on back roads so a SH150 would probably have been OK for me. If you are going to mix it a lot with traffic on dual carriageways/divided highways. You may have to spend a bit more and go up a size.
It always a compromise and a lot depends on budget.