Praise goes a long way in potty training a puppy. If you are outside training you may use a room to keep them in or a crate. The smallest size I would use would be the 18 inch by 36 inch. There is room for a bed, dishes and newspapers. If they are confined some hours they need more space than a little airline carrier.
Some people like to use a collapsible exercise pen to keep the puppy in during training.
This folds up flat for storage or transporting. They open up about the size of a baby's playpen. These are also wonderful for outside training for those that do not have a fenced yard. You just set it up next to the back door and put the puppy out in to it. If for outside use, I would get one atleast 36 inches high for Yorkies or Pekes.