Have you considered the pygmy corydora species? They include Corydora habrosus and pygmaeus. C. habrosus is a little bigger, like an inch and a half or less, and more like your traditional bottom-dwelling corydora. Pygmaeus is smaller, about an inch long, has a very smart pattern of black and white, and tends to school throughout all the levels of the tank rather than just at the bottom. I have a little army of 7 pygmaeus in my 15g and they are an absolute delight! Watching all seven move all around the tank is one of the hi-lights of my setup. They are also more hardy than panda corys and really cute. They go well with the smaller species that you are considering.
EDIT: here's a few pictures! I forgot I had these.