Boipeba is the island Morro de São Paulo used to be. It lies just south of Tinharé, separated from it by a river channel, and it has stayed small and quiet: a few sand lanes in the village of Velha Boipeba, some pousadas, and long beaches of palms and reef with almost no one on them.
The best of these are south of the village. Boca da Barra is at the river mouth by the village itself; beyond it, Tassimirim, Cueira and Moreré are a walk or a tractor-taxi ride away along the sand, with natural pools in the reef at low tide where you can snorkel among small fish. Moreré is a fishing hamlet with a couple of places serving grilled lobster and fish in the shade.
There are no cars on the island, and no banks worth relying on — bring cash. Getting here takes a boat from Valença or a longer crossing from Morro de São Paulo, and many people do Boipeba as a day trip from Morro on a round-the-island boat tour.
Stay a night or two instead: once the day boats leave in the afternoon, the island empties out and you have it almost to yourself.