Gday bush.
The best thing for you to do is get a bus to pattaya or a plane to phuket.
If your going for great nightlife, Im afriad bangkok just doesnt cut it anymore and youll be bored s#itless.
Depending on your budget....what I would do is go to pattaya for a week, the fly to phuket from there for the rest of your trip.
But if you can only do one, and seeing its your first time in thailand, maybe Phuket is the go.
As for traveling on your own, its no big deal, 90% of my trips I do by myself, theres allways some druken bum you can find to have a beer with (mai tai's full of them. LOL) and theres allways the cuties to get to know.
.
Rex