What a lot of love I got tonight from hubby and whiskey and billy! I am on cloud9! I hate that expression....au 7eme ciel is way better....I dont know what 9 stands for or is it from the popular Catch 22 book this expression?

Here is what I found in a search on google about this idiom

'Etymology. The origin of sense 1 (“a state of bliss”) is uncertain; however, the following etymology has been suggested: The first edition of the International Cloud Atlas (1896), which defined ten types of cloud, described the ninth type as the cumulonimbus which rises to 10 km (6.2 miles), the highest a cloud can be.' (source: google search)