We have had 3 Westies and loved them dearly. They require maintenance, just as any pet does. Ours were house dogs, so they had regular baths and brushing. However, they had issues with allergies here in the Houston area and needed prescriptions. Grass & fleas were the main allergy for ours. Since you already have large outside dogs, a Westie can take care of itself in most disagreements with them, because it is a heavier small dog. Yes, Westies are Terriers and are energetic, but our couch potatoes sure did like to cuddle, followed us routinely, plus gave us comfort at the end of a work day. They were good companions, plus, when they barked at a stranger at the door (we trained them to do that), they sounded much larger than a 15+ lb. fur ball. If we adopted another dog, we would get a Westie again.
Try the rescue places first, even for a pure bred dog. They'll appreciate you more. Good luck on whatever companion you choose!