If you're going to mix in an untreated room then you have to use references. Even if you know your room, you're still gonna want something to compare your mix to just in case. Eventually we should all strive to treat our studio spaces but obviously that's not cheap or easy to do. In the meantime it's best to utilize what you have and keep improving your listening environment progressively. This is especially important for beginners that are worried about mixing in an untreated space. Don't wait until you have the perfect room, get started now and make improvements as you go. Like I said at the beginning, use references and you'll get by.