One of the best ways to add thickness, creaminess, and sweetness to a smoothie without using ice cream is to use a frozen banana.
To add sweetness and thicken up this coffee smoothie, I use a bit of vanilla frozen Greek yogurt and either 2% milk or whole milk frozen in an ice cube tray.
If you’re trying to keep calories and sugar low, use skim milk and consider freezing vanilla greek yogurt.
To try and balance things out a bit, instead of using regular vanilla frozen yogurt or vanilla ice cream, I like to use frozen vanilla GREEK yogurt because it has more protein.