I, too, think getting an adult dog would be your best bet. That way, he/she is already trained, has a longer "staying power" than a puppy, yet you could still love, wrassle with and spoil him/her rotten on nights and weekends! AND adult dogs tend not to be adopted as quickly from shelters, so you'd probably be saving a life!

Speak with the shelter people, find out who the relaxed dogs are - as Mugsy said, it can vary from dog to dog, regardless of the breed!