Onesies for human babies work really well. Usually the newborn sized are just right for a 5-8 lbs dog. If your baby is smaller, there's Preemie sized ones, though they're harder to find. Here's a few pics of my Starr in hers after her spaying:
They seemed to work great, and they're easy to get on and off without hurting them, since they snap all the way up
