After washing enough plastic bottles, we opted to skip sippy cups. We’ve been really happy using jam jars! We started our now-toddler on a sample size jam jar (i.e., 1.5 oz: https://www.specialtybottle.com/glass-jars/clear-straight-sided/short-metal-lid/1-5oz-jam1) around a year old, then he moved to a 4 oz jar around 1.5 years, and is now on a 6 oz jar at age three. Our adult glasses are 8 oz, so he’ll graduate to that eventually. All of our jars have been “free” (i.e., the cost of jam, although I think you can get these for super cheap at craft stores), upcycled, and small enough that dropping them never causes problems!