As a fellow recovering people pleaser, I've found this such an interesting thread. Congrats OP on being articulate and self-aware, and lots of PPs for very perceptive points.
My tuppence-worth: while concepts of boundaries and matched energy are no doubt excellent and helpful, I think they're situation-specific, and become quite draining if used to support your whole approach to relationships.
Matching energies still allows the other person to define the relationship. There are times when you want to put in either more or less - to stimulate a new friendship, to care for a loved one needing support, to discourage unwanted attention. I find it more useful to think of what I really want to do, in terms of what I want to achieve, and do that- what others do and how much energy they put in is up to them. Similarly, boundaries, sure we should all have them in terms of no violence, stealing, unfaithfulness etc but most relationships are within those limits and defined more by a dynamic balance. Boundaries as a concept to define behaviours within relationships don't work if they impose an expectation others are required to conform to. We can't control what others do.
For me, a more useful way of thinking has been to imagine what I would do if I was confident,calm and clear on what I want -and then do it anyway.
I also notice how confident and assertive people act. Often they just don't care that much about awkward people's behaviour, so find it easier to be around them without taking much notice, or say no to them without it being a drama. I hope to achieve this attitude one day!