I would think that cottage cheese is closest to ricotta. Well, to be honest, cottage cheese very well could be ricotta depending on how authentic you are talking about the ricotta. Cottage cheese in the US really is the same recipe, only they leave the curds larger and add cream at the end. But cottage cheese varies from country to country.

And if you think Mozzarella is easy, you can do homemade ricotta with just milk and vinegar or lemon juice. Tastes incredible, but super high in lactose if you are lactose intolerant.