I got the honey bear cups off of Amazon when LO was 6 months to practice. They are pretty spill proof but it was more for learning as they have a really narrow straw and you can squeeze the bottle to help them learn to suck. He finally got the hang of it around 8-9 months. He will take drinks out of a regular straw now at almost 10 months.

Honey Bear Straw Cup for Babies 3 pack; 8oz straw bear cup with improved safety lid design; honeybear baby cup straw; honey bear cup and honey bear bottle. Straw therapy learning cup. (Blizzard-AQUA) https://a.co/d/hym0qlO

I just bought some different straw cups that are amazing. They don't leak and the weighted straw allows him to drink from different angles.

Munchkin® Any Angle™ Weighted... https://www.amazon.com/dp/B07L4DHNVK?ref=ppx_pop_mob_ap_share