The best thing about this smoothie is that you can make it thick or quite watery. For the thickest variation of this smoothie, I recommend using skim milk, protein powder, honey, and ice. Skim milk is slightly creamier than almond milk, so you will likely get a better texture but more calories.
Using ice cubes will also make a huge difference. Not only will your smoothie be a lot colder, but the consistency will be thicker. Knowing this, you don’t have to use a crazy amount of ice cubes because too many will dilute the taste.
If you’re able to, my favorite thing to do is freeze the watermelon and banana ahead of time. By freezing your fruit, you will not have to use ice cubes, and the flavor will not be compromised. Considering that watermelon has high water content, it will freeze fairly quickly and serve as a great substitute for ice. You can check out the video below to learn how to meal-prep frozen fruit for smoothies.