...two-strokes are the work of the devil! They're evil!! Run from these stinking, screaming abominations as fast as you can!!!
On a more serious note: You wrote that it's been years since you rode anything that small, and I've actually NEVER ridden anyhting that small, but have to say these bikes are lots of fun and some of them are all you need - around here. Had a Kawa 175 chopper, a 200cc Phantom, now I'm riding a CBR 150 R, did a one-day 700km trip on it - no problems! Always had a Wave on the side, still ride my old 11 to school every day.
Rent a Wave, the 125cc is quite quick and comfortable. if it's not enough, buy something bigger. For one-up long distance I can recommend the CBR; if your budget is limited, try find a Suzuki Raider 150 in good shape. You can get them for around 25-30K baht. 4 valves, DOHC, air-oil cooled, 6 gears.....