just thought i would let everyone know that target sell waterproof mattresses, up to a queen size. i bought one, it cost $45. i figure it may come in handy with leaky breasts afterwards as well (plus our mattress is brand new so i didn't want to riske ruining it).

other then that i have heard it suggested (cann't remeber where) to use a waterproof cot mattress protector on the car seat.