How do I know if I’m bigender or simply a masculine dressing cis woman?
I do have sexual fantasies about having a dick. Also could live without my boobs. But I don’t really have gender dysphoria.
How do I go about figuring this out without throwing myself into something I don’t belong?
Unfortunately, the questioning process for both gender and sexuality requires you to consider labels that might not apply to you, just the same as it requires you to consider labels that do apply!
Fortunately, there are plenty of reasonable folks in queer communities that are a-okay with people questioning their labels and coming to the conclusion that they had it right the first time.
If you join a particular community with genuine questions about yourself and an open mind, then the absolute worst case scenario is that you decide the label isn't right for you and now you understand a new group of people better.
That said, through personal observation I've noticed a lot of overlap between butch women and trans men [also femme crossdressing men and trans women, though they're less relevant to this question], and most of the difference comes down to the individual's personal feelings and examination of which differences matter. I'm in a similar place to you and for a while [had identified as pan since I was 15-16, didn't identify as bigender until 21-23] I thought I was a masculine woman, until I had a short haircut and was identified as a man by a stranger and realized it felt good.
So find the differences that matter to you, try out labels to see what feels best, and I wish you the best of luck in your journey!
-Mod Eli