Well, my aunt lived in an apartment and had a shih tzu, and a pomeranian. They were easy to train and very small. Some other suggestions are:
Chihuahua (Very small, and loyal.)
English or French Bulldogs (Usually small, but can be aggressive.)
Yorkshire Terrier (Small, but can be aggressive towards children.)
Welsh Corgi (Small, but are prone to back problems.)
Dachusaunds (Small, prone to back problems, not a good athletic dog, can hurt back severely if playing too hard.)
Beagles (They were bred for hunting! So watch out! Make sure you get the small size! There are very large types!)
Boston Terrier (Usually small, good watchdogs, don't really shed, and are very good with kids and adults!)
Italian Greyhound (Very small, very frail, they always shake like the Chihuahua, but they are great with kids!)
Jack Russel Terrier (Usually small, but havce boundless energy, they will tear your house apart if you don't train him very well!)
Minature Pinscher (Very small, have lots of energy, and great with kids, can be trained easily and loves to play!)
Pug ( Usually small, but loves to eat, prone to obesity, don't exercise him too much, or he may begin to wheeze! Just like bulldogs and other dogs!)
Shetland Sheepdog ( Can be small, but may be big! Have a very long coat! Must brush every day! Will shed! But make sure you get the right size! Great with children, very easy to train!)
West Highland White Terrier ( Usually small, but can be long doesn't shed much at all! Great with kids, and an amazing watchdog! has lots of energy!)
Thanks! But, remember.......pick the right one!
Signed:
-Peace.Love.Jonas.