Hey Ida, I don't mean to sound insensitive, but could you live without your parents being in your life at all?
You said that you already have a sizable and strong support network. Some people really can't live without their parents because no one else would support them either, and/or their parents are financially supporting them. But that doesn't seem to describe you or your situation. Please remember that relationships always go in two (or more) directions, even family ones.
Although they are and always will be your parents, you should respect yourself enough to not be involved with anyone who only hurts you rather than helps you. You are an adult and deserve to be treated with respect, especially by your parents. You may love them no matter what, but if they're just going to keep guilt-tripping you into acting the way that they want, and blaming you, then they're not respecting you at all. They're actually demeaning you; one could argue that it's emotionally abusive. And you shouldn't take that from anybody, least of all your parents.
In every relationship, there's some kind of power dynamic in play. You are no longer a minor, so your parents are no longer responsible for you, and you are no longer dependent upon them the way that a child is. By all rights, they should not have power over you, but they act like they do, which is why they've said the things that they've said. Probably because they still (and perhaps always will) think of you as their "baby," they assume that the power dynamic hasn't changed; the thought might never have entered their minds. But this is your opportunity to assert yourself.
Maybe an ultimatum is what's necessary. Plenty of transphobic parents cut ties to their trans offspring, but yours haven't, which suggests that having you in their lives is at least somewhat important to them. So if you threaten to cut them out of your life unless they try to respect what you're doing, even if they don't approve, then they'll be forced to reevaluate things instead of assuming that they're in the right and that you should bend to their will. This may sound harsh, but please consider how things will go if you don't try it: They'll never change their minds because they'll never have a reason to do so. You're already living on your own as a full-time woman with many loving and supportive people around you, so proving to them that you're serious and happy being MTF will not be enough.
If what ultimately happens is that your parents are out of your life for good, then don't think of it as a terrible thing, no matter how much it may hurt at first. You're already hurting now because of them, so why should you keep taking it for as long as they're alive? Do you think that you'd be better off with or without their hurtful influence in the long run?