I love sororities and am a huge advocate of them, but if this is your first time doing things properly, I wouldn't recommend it. They are a little trickier than a single betta. :) I would suggest a nice male with a school of little panda cories. :)
Cories are very cute fish and you can see them 'blink'. Their darker colours and swimming habits mean that they won't bother your betta and he shouldn't bother them. Given a sand substrate and a few hiding spots, they will be very happy.