Word or phrase to describe a couple that is perfect?
Solution 1:
To be made for each other:
- [of two people] very well suited romantically. Bill and Jane were made for each other. Mr. and Mrs. Smith were not exactly made for each other. They really don't get along.
(McGraw-Hill Dictionary of American Idioms)
Solution 2:
A match made in heaven.
This is a pretty common expression.