My first thought was that you should name/brand each business activity to be able to focus your marketing efforts more accurately. Your target market for your boutique will probably incorporate both your existting clients (owners of puppies bred by your kennel), as well as other toy owners.

You could separately name/brand the boutique "Daystar Dog Boutique" playing upon "night" and by day, they are out and about wearing your boutique items.

Both nighstarpups.com and daystarpups.com are both available. And you could "tie" them together with one slogan: Day or Night, your Pup is the Star.

Lastly, a website - consider godaddy.com to set up/design a website that is reasonably priced and can also host it for you. You could route both website addresses to a main page and allow the client to chose between the kennel or the boutique - making both types of prospective clients aware of the other side of your business. Additionally, make sure there is a link within each area of the website (the kennel or boutique) to get to the other part.

Good Luck!

*GG*