"What I am not so good at is feeling ok about having said no. I replay and justify the decision in my head, worry at it. I am going to stop doing that. From now on I am going to work on 'no, thats not for me' and leaving it there."
yes. the focus in this kind of "no" is on you, what is okay/positive for you and what isn't. when saying this kind of "no", it makes no judgment about what others are doing; it has no relevance to them as such.
the fact that they then sometimes make your "no" about
them is a different story and not about you, though it might sound that way.
well! haven't i just given myself a good talking-to