I think a lot of different lighter shades of pink and purple would work. Yellow too. Even a peach or coral kind of color. Maybe a light shade of blue? Light gray even. A lot of these options would be gorgeous alongside the navy blue!
I think navy goes with pretty much anything! My guys are wearing navy and my girls are wearing a purple/pink color (wisteria on Azazie). Our florals are going to be all different shades of blues and purple/pink.