Yes, I think that [name]Belle[/name] can stand on its own! In fact, while I really like [name]Isabelle[/name], [name]Anabelle[/name], [name]Mirabelle[/name]… I really love [name]Belle[/name] all by itself.
Of course, that could also be because it is a family name. My great-great-grandmother was [name]Belle[/name] and she was a fiery redhead that lived to be 103. In fact, I was 6 when she died. Because of her, I have a great association with that name.
On a side note, that particular part of my family has really awesome names. And many are getting pretty popular. [name]Belle[/name] had two children, [name]Lula[/name] and [name]Royce[/name] (g-gpa). [name]Royce[/name] married [name]Ava[/name] (yep, that spelling and she was born before [name]Ava[/name] [name]Gardner[/name]) whose mother was [name]Josephine[/name] (nn [name]Josie[/name]).
If you like [name]Belle[/name], then go with [name]Belle[/name]. My only adivce would be that if you have a one syllable last name that it may not be the best choice. Also, you would probably want to go with a longer mn.