как сыр в масле

см.
[in clover]
[ride the gravy train]
[live the life of Riley]
[high on the hog]
a bed of roses

sitting pretty (in a good position, in favorable circumstances; in a favorable position; be successful) —

Example 1: Rich in oil and timber resources, Alberta was sitting pretty. (IdiomHome)

Example 2:
A: Have you talked to Randy lately? He just got a new job and a raise.
B: Yes, I've heard. He sure is sitting pretty.
(openenglish)

see also
[catbird seat]