Dogs are cool. In August we got a chihuahua mix that weighs in at 6 whole pounds! My girlfriend wanted a lap dog this time around (our last dog was an 80 pound German Shepherd). It sounds like your weather is much like ours, though. The problem with a very small dog is the fact that snow & cold are an issue. The snow gets too deep & there's not much hair or mass to keep Papi warm. Thus, getting him to do his business outside in the winter is a problem. Another issue to consider is that dogs tie you down more than cats do (though I'm not a big fan of cats). Just a few thoughts from a chihuahua mix owner...