Laura, thank you very much for your timely comment. I saw it just before I went to my sewing room to cut a new muslin! I had traced the size 12, tapering down to 14 and did the fba when I read your comment and thought "I will try that first". A little later this is the result.
I was happy with all comments of course, and the general opinion was (like I thought too) that I could have started with size 12 in the shoulder/neck part. Again, only the right side of the jacket is changed.
I'm wearing a thin lambswool top underneath, and think I won't wear anything with more thickness under this jacket. It feels a bit snug, but like Lindsay T said, this is meant to be a snug fitted jacket. Am I ready to cut in the real fabric?
On the right is the new adapted version. For comparison I have put the pictures side by side.