I’m not a huge fan of any kind of supplement if you can get the nutrient elsewhere. When it comes to protein, you definitely can, even as a vegetarian! Here are some great sources:
All dairy products are complete proteins, meaning they contain all necessary amino acids, along with buckwheat, amaranth, spirulina, soy, and nutritional yeast.
If you still can’t get enough from those sources, try a protein powder, like whey, hemp, or brown rice.