Sri Lanka is India 'Lite'.
I have never been to Unawatuna but I have heard it's a wonderful place with a great beach. Also near Galle which is very nice town too.
Trains are a great and very cheap way to get around. The train station 2km from the airport doesnt go to Galle so you would have to get a train to Colombo which is in the opposite direction. May be worth getting a taxi for ease. You will have no problem getting one. I can't remember the price but I would say no more than £15.
Mozzies like to chew on me. Not a major problem apart from one hotel where they had a lagoon and fish ponds.
Have a look at seat61 dot com
The tea factories are OK
The Elephant Orphange is great
Spice gardens - ok for 20 minutes
If there is a turtle hatchery and you are there the right time of year they are good.
Kandy is a nice city/town. Just getting there through the hills is great. There is the botanical gardens, temple of the tooth, the elephant orphanage nearby, other temples. Lake, Gem shops and craft stalls so it's a good base for a few days. The World's End in Horton National Park is supposed to be well worth the climb.
Colombo is a nice city and well worth a day shopping / eating. Has very reasonably priced hotels and will get you back near to the airport.
Best bit? Just wondering around on foot.
Hygiene. No worse or better than India. Drink bottled water, watch the ice and any fruit / veg that may have been washed in tap water.
The only problem you may have with finding hotels will be in Kandy if there is a festival on. It may be worth checking expedia etc., for an idea of prices and then finding a travel agent in Galle to see what they can do. You can always book somewhere online whilst you are there. You will have no trouble getting a driver - they all know what tourists want to see. Find one that speaks good English, tell him where you want to go, ask him for sight seeing suggestions and fix a price. All hotels can get drivers no problems.
I am going back Nov or Dec this year!!
Enjoy