Well, I knew someone that had a boxer. I, myself, wouldn't want one in the house with a yorkie, but that is a judgement for you. I read this:
Boxer Temperament
What's Good About 'Em,
What's Bad About 'Em
By Michele Welton. Copyright © 2000-2010
The Boxer is usually animated and playful, though some adults are more deliberate and dignified.
Exercise needs vary from vigorous romping for high-energy individuals, to long daily walks for more sedentary Boxers.
Most Boxers make vigilant watchdogs, though guarding and territorial instincts vary. Reaction to strangers varies from "Hi there! Come on in!" (often accompanied by enthusiastic jumping), to sensible and polite, to wary, even challenging. Early socialization is important to develop a stable attitude.
Many Boxers love children, though most are too exuberant for toddlers, and while his reputation for stoicism is deserved, some can be grumpy in response to mischievous kids.
Some Boxers love to play with other dogs, while others can be dominant with those of the same sex.
Consistent leadership is a must, as the Boxer is a strong-minded working dog, but obedience training must be upbeat and persuasive rather than sharp. This breed is stubborn, but also sensitive and proud, and may shut down if jerked around.
If you want a dog who...
•Is medium to large and well-muscled
•Has a big muscular head and short face
•Has a sleek easy-care coat
•Is steadfast and reliable
•Makes a sensible watchdog, and looks so imposing that he is an effective deterrent even when friendly
A Boxer may be right for you.
Boxers: What's Good About 'Em? What's Bad About 'Em?