I went to Sri Lanka in March last year, found it truly amazing. It is an island that offers everything and more. I was travelling on my own and felt safe apart from in Colombo. The day I got there the Tamil Tigers did there first attack from aircraft and the military presence in the city was immense. A lot of the island you just don’t go to, and unfortunately this includes some of the best dive sites and beaches. But all is not lost as there is a lot of beauties…….
I then got a train (very cheap and scenic) to Hikkaduwa. You can also get a taxi which is also cheap, I think about 30 pounds for a 4 hour drive. I stayed at Mambos,
http://www.mambo.nu/, which is a surf place, run by some really great guys. It was the most luxurious back packers place I have ever stayed in. Very cheap and the guys will help you with anything you want. The best room is a massive double bed, shower etc. with sea views so you can see the sunset. They even put joysticks outside your rooms in the morning. Even this room is really cheap!!! You could of course, get much nicer accommodation, but I am not sure where. I seem to remember a lot of eco friendly lodges advertised.
The water was 28 degrees, turtles everywhere, beaches v v clean and stunning!! Diving is good (http://www.divesrilanka.com/), and as I say you can find everything here, beaches, culture, history, brilliant locals, shopping etc. Kandy is also a nice town.
Day trips - Galle, the town nearby Hikkaduwa
Hikkaduwa turtle nesting or sanctuary (but a little basic and run down)
elephant orphanage (http://www.youtube.com/watch?v=yBKe9-9smB0&feature=related)
Also have a look at the government website, which has lots of interesting things!! Let me know if you need any more help!