Navy is very chic. Regarding the dresses you posted I think there’s a good chance you’ll absolutely boil in them in June - where’s the wedding?
If the weather is warm you might not need a jacket or coat. I still think a pashmina/scarf is nice with a long dress for later in the evening.
I love (wish I had a wedding to go to!) the first Whistles dress posted. It would look lovely with sandals, a suede/unstructured clutch bag, and a saucer style straw hat. How tall are you OP?