Lolly this is a major question for everyone who survives abuse and recognises that they have an ongoing problem because they default to victimised roles.
I have always believed that we give out a signal of some kind - and not just to potential abusers! I have made a number of women friends who have eventually revealed that they also have been subject to narc parenting/abused childhoods. Either it is far more common than we assume, or there is an internal beacon.
I really recommend looking at the Stately Homes thread and reading about other peoples experiences. If nothing else, it will reassure you that this is a problem many have to cope with.
For me, therapy taught me to look at why I react as I do. In understanding the "why", you develop the ability to question your reasoning. And with that, comes the ability to change the reasoning.
For instance, realising that being a people pleaser is rooted entirely in well learned lessons that keeping people happy keeps you safe, means you can pause before answering anything .....and ask yourself if you are agreeing because its right, or good for you, or because you will feel at risk (of losing the friendship/hurting the person/losing something) if you say no.
Usually, it turns out to be the fear 
There are two other tips that may help.
The first is that you need to believe that it is OK to say 'no'. People worth having in your life are not there just because you always say yes. People that actually care about you will be just fine with hearing 'no, that doesn't work for me'
The second is to stop seeking approval for your decisions. That is really hard, and I found the best way was to have just one person (who will never abuse you, and who you trust utterly - I use my adult daughter) and when you feel a decision needs to be talked through (every single one for me, when I started)....only discuss it with that one person. Because you do not need validation from other people. What you think is right, is right for you. Truly!!
It is really hard to put that level of self-approval into place, but it is a key to changing how you feel about yourself, and the way you signal to others. The only thing which perfects it, is practice.
Its a long road, but I think you are already moving along at a pace, Lolly. Your post shows a lot of self awareness, and a lot of understanding about root causes. That is more than half the battle
