This idiom describes someone who is very comfortable and enjoys a life of luxury and ease. It is often used to describe someone who has a lot of money and doesn't have to work hard.
The phrase originates from a 19th-century American poem that depicted Riley as a carefree and wealthy man.
Here's how it's used:
* "After winning the lottery, she's been living the life of Riley ever since."
* "He's got a good job, a nice house, and a family he loves. He's definitely living the life of Riley."
While "bread well buttered" isn't a common idiom, it does convey the idea of comfortable abundance and is often used in a humorous or informal context.