I prefer to do most of my training in racing flats (actually, all of it in nice weather, but in winter I switch to trail shoes). Shoe companies mostly only produce flats in mens' sizes (sometimes they call them "unisex", but they are built on a mens' last and sized like mens' shoes). I wear a 7.5 street shoe and a size 8 women's running shoe (sometimes 8.5). I'm completely comfortable in size 6.5 -- 7.0 men's flats -- I have narrow heels too but the smaller sizes seem to be scaled down appropriately.

So I would definitely not be afraid to give men's shoes a try.

Good luck!