Kate, I use as large a pot as I can find. Usually not smaller than 2 to 3 gallon. Also, make sure you get soil especially for containers because they have to be watered constantly. Sometimes twice per day in Tennessee.
Also, there are smaller bush type plants. I have seed for Bush beefsteak and the small cherry type tomatoes. I found a tomato called Umberto Pear tomato. They are small, about the size of a golf ball. They were almost extinct. I can only find the seed at "Totally Tomatoes". I have very good luck with them. They are an heirloom.
Yes, I am using small, choppy sentences.