Button-ups can gape, which tends to be awkward.
Personally, I would choose a sleeveless shell with a neckline at your collar bone or 1-2 inches below, avoiding V-neck styles because inadvertent cleavage.
It depends a lot on your complexion, but with navy I like plum or olive for darker complexions and light blue or even pale yellow for lighter complexions. Just please not red. You are not trying to be the president.
Also re: brown shoes. I know navy suits & brown shoes are a big thing in the world of men, but as a female, I'd pick black before brown but cordovan before black.