I breastfed, but gave water in the cup. Just little sips when he got his purees. I weaned him when he was a year bc I was pregnant so when I switched over to milk in a sippy he did great. Then we started using the tommy tippee super star straw cup, that one is great for not leaking and working at just about every angle they can tilt it to.
We shifted to a weighted straw cup/360 cup and started introducing between 10-12 months. We introduced for water and gradually shifted milk to those.
I started with the nuk soft spout trainer cup at about 6 months