Originally Posted by Guy E. Trepanier
I could change the 3rd line of the chorus for

With you I'm so happy or You're the right one for me

I don't know. That might break the rhyme scheme.
My idea was:

You're my little sunshine
You're my fantasy
You're my little sunshine
You mean the world to me or something else that rhymes with "fantasy"

Alternatives:
You're where I want to be
You're my melody
You're my gravity
You're my harmony