I just bought 2 Paws Aboard 'Louie's for my guys. They fit really well. I've had others for small dogs before that fit like lumps! Also, these have a mesh panel under their bellies rather than just straps. I always worried about picking them up and having them supported on two thin straps cutting into them!
http://www.pawsaboard.com/dog-lifeja...jacket-xxs.asp