read the various threads already created about breeding bettas.
they're not livebearers.
breeding bettas is a complicated, time-consuming and expensive project.
you can't breed petshop bettas either, and definately can't keep them in the same tank.
I'm fairly new to bettas myself, so can't tell you what to look for when choosing a female. However, I don't think you can keep them in the same tank unless it's pretty large and heavily planted, as she'll need lots of places to hide.
You'll get the real betta lovers on later, once work has finished, and they'll be able to answer your question in a flash!