I know it is a little bit too late to share one of the best Taiwan's Coral Island in this kind of sweater weather. But since Taiwan do not really has fall and the winter here is not too cold, I think you can try to have some beach vacation during fall-winter season.
Little LiuQiu is the only Island that I have ever visited in Taiwan archipelago (of course beside the main island). I went there by boat from DongGang Harbor from Pingtung county. This island area is only about 6.8 km². Therefore, you do not really need a tour guide. Tourist usually rent a motorcycle and stroll around by themselves. It only takes about 2 hours to explore the whole island.
