If there’s one thing you plan on doing in Santorini, let it be this!
What happens in Mykonos, really needs to stay on Mykonos. But you CAN have a restful stay on the island, if you prefer!
Syros is for your more authentic Greek island experience.
Kefalonia is among your lesser-known Greek islands, giving way to Santorini, Mykonos, and Crete among others. This is exactly why you should visit this almost ethereal place.