When I made my puff quilt, I just kept putting the fluff in until I thought it was the right amount. Then I pulled the fluff out of the biscuit to give me an idea of how much it was. I eyeballed the rest of them after that. Be sure that you don't over stuff them and make them firm. You will have a devil of a time sewing the puffs together if you do that! I bought a really nice poly fil at Joann's. It cost about $8 bag but it has a soft silky feel to it. I think it had "Silk" on the label.
ETA: Found what I used. It is called Silky Soft.
http://www.joann.com/24-oz-bag-of-si...4&prefv1=false