With my little one I mixed just a small amount of breastmilk with water and cereal. I, personally, waited to introduce juice until my daughter had stopped weaning, but that is another option. If you do that, just use a little bit of juice (like a spoonful or two) and mostly water.
I know other moms have used unsweetened rice milk, but I never did. As for pumping, I found that I was most productive first thing in the morning. Have you tried breastfeeding on one side while pumping the other? That always helped me get quite a bit more as baby helped with the let down.
Good luck!