I also use the Yo Baby yogurt and have found it at Super Walmart or Super Target and many other grocery stores.
Also, for cheese, I have found cheese crumbles (in cheddar or mozzarella or a combo) to be good finger foods. I have to cut up some of the "crumbles" because they are a little to big but they're easy for my lo to handle and he loves them. They are in a package just like shredded cheese and at least at my grocery store, included with the shredded cheese.
As for age, I too, think I waited until 8 months to introduce yogurt and cheese.