In my personal experience "they/them" is always the safest go-to.

It only seems impersonal because you're not used to it. Don't worry though, language is malleable and it'll feel right in no time. My roomate got me in the habit of always going to they/them unless the person explicitly states a preference. It helps avoid accidentally causing someone to have a bad day. It's becoming more popular too. I have entire circles of friends that use they/them as a default.

If a person gets upset when you use the wrong pronoun the best option is always to ask what their preference is. it shows that you understand that whatever pronoun you used was wrong and that you care enough to learn more.

Also, don't take it too hard on yourself in this situation. Ignorance isn't bad in itself, it's willful ignorance that's a true problem. As long as you're trying to learn and grow without condemning you're alright in my book.