Santa lives here, very jolly! (2,3,2,3,5)
I believe the answer is:
on top of the world
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for on top of the world that I've seen before include "as Hillary once was?" , "Penguins aren't" , "happy" , "Delighted" , "In seventh heaven" .)