I went into Target looking for nursing-friendly dresses for summer. I didn't find many dresses but found these rompers that have simple hook-and-eye closure in front and pull to the side super easily. Bonus, they're BOGO 50% off right now.
(Don't mind my dog's butt photobombing me.)
https://www.target.com/p/women-s-surplice-romper-black-print-mossimo-supply-co-153/-/A-51732466