I remember How clean's Aggie and Kim standing a mattress upright and rubbing it with a dry bar of soap to get rid of urine and smells. I think they left it then wiped or hoovered it, can't remember? Sprinkling bicarb on and leaving this a while helps smells.
DS2s mattress is a bit stinky and I put stuff on but waiting until he's totally dry and then buying new mattress.