Yeah, I think that's pretty much all that is generally needed. I've had people assume but ask me first, just asking "she/her?" as a question, I respond yes, we go about our business. If you don't want to assume, you can also pretty much universally use they/them in passing, or if it's someone you interact with more frequently, people really don't tend to mind if you ask.

I mean I'm trans, I get around quite a bit in queer spaces, I haven't met anyone who would get super mad about initially assuming pronouns rather than just saying "hey I prefer XYZ" and moving on. Generally when people react strongly to being misgendered, it's due to ongoing conflict over their identities, having to deal with people who use pronouns to casually disregard your Identity, familial abandonment, etc. It is often a response to complex trauma from elsewhere. That's not really your responsibility, but I've been there and if you can offer them any grace in those moments, it's extremely helpful.