How far you've come! I hope others who are not as far along the path as you will be able to realize some of what is necessary to progress.
Children who were abused often have the same basis for their reactions in adult life. Normally, there are boundaries set that are good for all in a family. Each person has their own personal space and amount of respect that no one "should" trod upon...and if they do, it's a mistake that is apologized for and forgiven.
When a child grows up in an abusive home, there are no personal boundaries. Others might have them, but the one being abused is stripped of all sense of ownership. The rules also seem everchanging, thus they never know when it's safe to speak, act, want etc. There are no boundaries for them to stay behind or for others to have to cross.
Setting boundaries in life is a good thing to do, imo. Sometimes not knowing how or what is allowed or even if they are capable of realizing and holding to any boundary keeps the emotional life in a state of upheaval. I think seeing a therapist (T) to help find what is the "norm", what is acceptable to expect from others and yourself can help.
When someone finds themself reeling from what another has supposedly done to them, and not knowing why "these things happen to them all the time" then a lack of suitable boundaries might be the culprit, don't you think? (I say supposedly because not all such events are really breaches of a boundary.)
For anyone beginning, I again suggest to start small, with little things that might not mean anything to another person (and thus they won't notice anyway.) If you live with others, then it could be to lock the door to your bedroom from time to time, even, say, when no one else is home.

It could be NOT eating something someone else wants you to taste, or not watching a movie you don't wish to see. Those are boundaries you set for yourself. Ongoing boundaries, like some you mentioned KD, are quite acceptable, and we all have them (or should, and feel comfortable with them.)
I have some that others find silly, some are just plain good. I won't drink and drive. Not even if it's a glass of wine with a meal. (Unless it's a very long time and a very big meal before I would have to drive a very short distance.) I insist that anyone riding in my car wear their seatbelt. I don't allow strangers into my home. I won't be roped into doing something silly for a game that I really don't want to do. I pay for and get my mail at the post office rather than my home.
Perhaps ppl who feel like they have no boundaries can realize that they might after all, and then feel good that, "Hey! I can set boundaries and feel safe and better about myself."
TC (hope I didn't hijack your thread)