The Mauritius Command by Patrick O'Brian (1977) is the best novel set in the island's waters — one of the Master and Commander series, following Aubrey and Maturin during the Anglo-French struggle for Mauritius in 1810. Excellent even if you haven't read the others.
Mauritius, Rodrigues & Réunion by the Rough Guides or Lonely Planet are both solid practical guides, updated regularly. The Lonely Planet is more opinionated; the Rough Guide has better historical background.
The Dodo's Fate and similar natural history titles explore Mauritius's extraordinary ecological story — the island lost the dodo, the Rodrigues solitaire, and dozens of other endemic species following European settlement. The current conservation work to save the Pink Pigeon and echo parakeet is one of the more encouraging wildlife recovery stories of recent decades.
A l'Ile Maurice by various Mauritian authors in French or Creole offers a window into island life that most English-language travel literature misses. The island has a lively literary tradition in both French and Creole.