You can certainly add yogurt, but if you do we suggest not using banana. As we mention in our basic green smoothie recipe, we use either yogurt or banana as the creamy base.
There are so many fruits that work great in a green smoothie! Try banana, all types of berries, mango or pineapple, stone fruits like peaches, cherries or plums, apples and pears are great too, and you can even use oranges, avocado, and grapes.
You can make green smoothies with water, milk, coconut water, almond, soy or coconut milk, and even juice. However, juice has added sugar, so keep that in mind when choosing.