Hi, I know of a fully-furnished apartment for rent in Colombo.
It was previously occupied by a friend of mine and he highly recommends this place as it is located in a superb neighbourhood that is extremely peaceful, safe, convenient, and close to all major locations of Colombo.
Also the owner is a very nice person. It's got 2 bedrooms (a/c), hot water, internet, satellite TV, etc.
The price is also extremely low at only Rs.40,000 per month.