(possible)transgender pronouns

I know there's a specific forum but I'm not sure if I'm supposed to post there.
Is 'they/them' the least offensive pronoun in a situation where you don't know how someone identifies? I've developed a bookbuddy relationship with someone I kept bumping into at the book store. We always have great conversations and have a lot in common. Last time we bumped into each other we went for coffee afterwards and a situation came up where a pronoun was necessary. I was able to use 'ours' luckily. I would be uncomfortable at this point if they asked *me* a personal question, so asking them isn't really an option. I don't even know if they are transgender or not. They dress androgynous(ly?) and have a gender neutral name. Am I just overthinking this?

Maybe. In an ideal world we'd just see a friends as another person, no gender, no color. But I do understand and hope it works out.

thanks George
The thing is - it doesn't matter...I'm just worried about inadvertently offending.

I think that "they/them" in the singular sense is the closest thing English has to a gender-neutral pronoun. Hopefully as you get closer to your friend, they will reveal their preferred pronouns to you. Before they do that, they can't be offended if you use the wrong ones. There is really no way to know unless you are told.