Thanks again, all! You are all so generous to weigh in here; I haven't been on the forum much of late, certainly not posting photos. My daughter has my real camera for a class this term...
Marilyn, Massimo Dutti sizing seems to be like Zara sizing. I normally take an XS in places like Banana Republic and a small in Zara. In this case I ended up taking the medium jacket. There really wasn't much difference between it and the small at all in the shoulder or even the sleeve length/ width. It seems to fit quite small overall.
I wonder in fact if the sizing is consistent. They only had the one for me to try in each size, so I don't know. There was a flaw in the small jacket inside the pocket, which is another reason I went with the larger size. I'll try it on at home again just to make sure. I can always exchange for a small if it seems too big on reflection.