To be honest, I would try breastfeeding again if I were you but enlist the assistance of a lactation consultant. The closeness that baby gets from breastfeeding is very beneficial, and if you can get things going, it's wonderful for you too.

But if you don't want to do that, I would say definately express instead of formula. I highly recommend getting an electric pump though, I have a manual one and I need to keep one breast full all day to get just one small bottle! With an electric one, you just turn them on and sit back, i believe. They're expensive (which is why I got a manual one) but you can pick up some second hand ones around the place (which is fine as long as you sterilize them) and the breastfeeding association rents them out.