My honest opinion is that most of the cultures where the thumbs up has a history as an offensive gesture have enough Facebook and YouTube users and enough exposure to Hollywood that they understand you aren't telling them to go fuck themselves.
But if you really do need a new gesture... I dunno, the thumbs up is polysemous so there's no real one size fits all replacement. But at least in some senses you may be able to replace it with something like the international fingerspelling of O-K.

