Can't help with the mouse pee, but you need to go to an upholstery shop or upholstery supply place to get the foam you need. CHECK OUT THIS THREAD
You should use a firm foam, at least 65 compression to re pad the seats. Foam has a 4 number designation, the first 2 numbers refer to the quality, and the 2nd 2 numbers refer to the density. The higher the first 2 numbers are the better the quality. The higher the 2nd 2 numbers are the firmer the foam. 2665 or 2680 would be good choices. You can use softer foam for the seat back, 25 to 40 compression would be fine. Be prepared for some sticker shock as far as the price goes, good foam is not inexpensive. You will also end up with a far better seat if you put a good deck pad over the top of the seat springs to protect the foam from being cut by the springs and edgewire that holds the springs in place. Check out this thread DECK PAD
You can get a deck pad from an upholsterer or upholstery supply house also. Do not put cotton batting in your seats, the cotton makes for a perfect place for mice to make nests. There are lots of synthetic alternatives ( like Dacron Polyester fiberfill) to cotton as a filling and padding material. I did a '49 Packard, and mice had filled half of a headliner section with cotton they had scavenged from other places in the car.