Lonely Planet Brazil or Moon Brazil — either of the major travel guides covers Florianópolis and the Santa Catarina coast well, with practical information on beaches, transport, and the island's neighbourhoods.
Little Brazil: An Introduction to Brazilian Culture by Dário Borim Jr. — a readable overview of Brazilian culture, identity, and regional differences that helps contextualise how distinct the southern states — with their German and Italian immigrant heritage — are from the rest of the country.
The Passion According to G.H. by Clarice Lispector — one of the great Brazilian novels, by the country's most important 20th-century literary voice. Not about Florianópolis, but essential reading for anyone wanting to understand Brazilian literature and sensibility.
Surf Brazil: The Definitive Guide to Surfing in Brazil — a photo-heavy guide to Brazil's surf culture and coastline, covering the south's consistent swells and the communities built around them, including Florianópolis and the Santa Catarina coast.