I now say “my former husband;” I really don’t like the sound of “my ex.” While I was in the process of divorce, I would say “my soon-to-be ex-husband,” if the need ever arose but mostly “Joe” would suffice. Or interrupt myself, as in “My husband, Joe—we’re separated—will be here in an hour” or whatever.
Since I don’t like “ex” I found ways to get around saying it. Usually just his name worked; most everyone I had reason to mention him to were well aware of the status.
For you, if they’re not apprised of the situation, and it doesn’t matter, I would think “ex-wife” would suffice unless you feel the need to be completely honest with strangers.