"Get one's leg over" is a crude and vulgar British slang term for having sex. As such, there are no polite or formal synonyms for this term. However, there are some variations of "get one's leg over" that are slightly more acceptable or at least less explicit. These include "have sex", "sleep with", "make love to", "romp with", "bed", "copulate", "mating", and "intimate relations". It's important to remember that any word or phrase used to describe sex should be used with respect and sensitivity towards others. It's always best to keep language appropriate for the audience or situation.
