WHAT SIZE AND FLOW CSP DO YOU NEED
A disposable is usually about 9-10" and night pads 10" - 10.5" and this is a very good guide to go by.  If you feel a disposable is to long go shorter, if you feel its to short because you bleed off the top and/or bottom go longer. 
Choose a flow that suits your needs the same as when purchasing disposables.  At Crimson Moon we offer Lights, Regulars, Heavies and Supers. 
(Our Supers are also suitable for postpartum bleeding)