Hi Loving---You can put just about anything you want to in a smoothie. You will want to be careful of the source of the protein. I would avoid any milk proteins, whey/casein, and I can explain why later. Just go to www.pcrm.org and put dairy in the search box to start. I will send you ingredient information on a protein mix that I use and my doctor loves. I will also send you a recipe for a smoothie that I got from a Naturopath who has her PhD in Nutrition. The superfood ingredients that it contains, outside of a banana and berries, is green tea leaves, a specially grown for food brewers yeast (for those energy packed B vitamins) and ground flax SEED. You want the seeds, as those contain lots of protein and fiber, vitamins and minerals and a compound called lignans, which contain cancer fighting compounds, as well as those wonderful plant-based omega 3 fatty acids.
I could send you samples of the protein meal replacement powders. It comes in french vanilla and dutch chocolate. My husband likes the chocolate with choc almond milk, almond butter, a little mocha powder and then we blend with frozen coffee ice cubes for a coffee mocha/almond flavor. Again, there is no end to the combinations that you can put together. My kids like berries, but I like orange/pineapple/mango juices with frozen tropical fruits...maybe with some coconut as well.
I'll talk to you soon. Be well...D.
PS. I can help with strategies to get more fruits and veggies into the diet also.