I've successfully cleaned a mattress using spray upholstery shampoo and then drying it with a hair dryer. I've also set a heater with a fan on the bed far enough away from the spot that the heat hits the spot. You have to be careful when using a heater. If it doesn't automatically turn off when tipped over, I'd not use it.
BTW, I bought a terry fabric mattress protector when I bought my mattress. It's coated with something that makes it water proof. AND it is soft, doesn't crinkle or make for sweaty sleeping. It was $60 but so worth it in comfort and protection.