Off the shoulder tops and dresses are in at the moment. You can wear the tops with pretty much anything, there are a lot of cool looser styles around as well as tighter ones that could work under dungarees. To breast feed the neck can be easily pulled down (dress) or a top can be pulled up (worn with lycra boob tube underneath).
I recently posted a photo of me wearing The Honey dress from the AG Jeans Alexa Chung collection. Its a really cool dress, loose fitting and flattering. I wore it with trainers but i expect i will wear it with sandals and wooden heels to.
Showing your shoulders off can be a nice and flattering way of exposing a bit of skin and feeling summery without feeling to naked/ exposed.