I'm not sure if you can bring somebody on cloud nine. But it's used when somebody is extremely happy, especially because they're in love!
'I feel I'm on cloud nine today!'
You can also say, 'I'm over the moon!', 'I feel on top of the world!', 'I'm in seventh heaven!', 'I'm thrilled to bits!', 'I'm chuffed to bits!',...etc.
- For Teachers