There are just seven one-island countries. What are they? These are countries that (a) don't share part of their island with any other country, and (b) have over 99.5% of their territory on a single island.
From Wikipedia: The fourteen British Overseas Territories are territories under the jurisdiction and sovereignty of the United Kingdom, but not part of it. However, if you believe Turkey, which asserts that Northern Cyprus is a separate country, then Cyprus would be disqualified for that reason (we don't disqualify it though, because we agree with the remaining 203 nations who say that it isn't!).
I don't think Curacao qualifies as a country since the residents are considered Dutch and, along with Aruba and Bonaire, they are part of Kingdom of the Netherlands.
Yes, Curaçao is a part of the Kingdom of the Netherlands - which is exactly my point. It is a part of the Kingdom, not the country of the Netherlands. The country of the Netherlands is sits alongside Curaçao, Aruba and Sint Maarten as one of four constituent countries in the kingdom. Ergo, Curaçao is a country.