I think using the pads is fine, I would maybe upgrade to a litter box. As long as your dog isn't going anywhere else in the house I think there is no reason for you to train your dog to go outside. If my dogs were smaller I'd use a litter box, especially in the winter, because its easier to clean up and the dog has access to it at all times. I wouldn't get a dog door because I like to supervise my dogs outside at all times.