Best cup for 5 month old?

My babe has been primarily bottle fed (breastmilk/formula combo) due to production issues. I know this can impact the formation of his palate and oral musculature. I understand cup drinking can help with that and he’s about to turn 5 months. He doesn’t have signs of readiness for BLW yet but is holding his bottle so I’m wondering if I can start introducing a cup with small amounts of his breastmilk/formula combo. What do y’all think? If you’ve introduced a cup at 5/6 months, which cup would you recommend?