Boba (or tapioca balls) are the default mix-in for milk tea drinks at Saint's Alp Teahouse, but I love to swap in something slightly lighter: nata de coco.
Most often found in Southeast Asian desserts, nata de coco is essentially a jelly made from fermented coconut water. Cut into tiny cubes, it's chewy and a bit firmer than jello. Each slurpable bite is cool and significantly more refreshing than tapioca.
Make sure to give the drink a stir before you sip—nata de coco quickly sinks to the bottom of the cup.