Just multiply your pledge amount by the number of the quantity you would like. ...Want 3 pairs of the Early Bird Standard Grey ($25)? Simply pledge $75.
A few things to consider...
CLOSED TOE slippers are a bit warmer, great for the upcoming winter. They also hide your toes if you are feeling a bit self conscious about them. ;)
OPEN TOE slippers allow the toes to be exposed and they 'breath' a bit more. Not the best if you are trying to stay warm.
Don't see the answer to your question? Ask the project creator directly.