Average highs for Mauritius are around 24 degrees so might not be hot enough for some, but it will be a pleasant temperature for relaxing on the beach. Evening temperatures may drop somewhat so extra layers may be necessary for al fresco dining or sitting out on the beach after dark.
June sees the start of humpback season off the coast of Reunion Island which allows you incredible wildlife sightings but despite this obvious draw, the island remains fairly quiet. Therefore lodge and hotel availability is likely to be good. Most days will be dry and temperatures will be cooler up in the mountains which makes it an ideal time for hiking.