I think
Bella is a bit too common and therefore boring to me. Therefore I definitely wouldn't use it as a name on it's own.
I think
Annabel is a good choice.
Bella is still a logical nickname and you prefer it. I think
Annabel is nicer than
Annabella (just less frilly) - and they're both better than
Isabella. I don't know any Bellas but I think a lot of Isabellas go by
Bella.