Learn to drink cups/straw cups

Kay

What is the best cups to use for a breastfed 5 month old that refuses bottles and pacifiers? From watching us when she sees a cup she opens her mouth and mimics drinking so I was thinking it would be easier to just try to transition her straight to a cup, but what would be good options to start with? Preferably something easy to clean that doesnt leave spaces that are hard to reach that will create mold.