Want a small LAP DOG? thoughts on west highland terriers (WESTIES)???

in the past ive had a lab, a brittany spaniel/pit bull mix, and a chihuahua......ive loved them all!! this time i want a dog that likes to excercise but can also just chill out with me sometimes. it needs to be a dog that can spend about three hours a day in my backyard (even tho it will be an inside dog). i really want one that isnt horribly hard to housetrain tho i know no dogs are easy.....what about a westie? any thoughts? thanks in advance!!