Is there any way to get the smell of pee out of my stepdaughter's mattress?

My stepdaughter is 5, and has begun peeing the bed again nightly. I work 24 hour shifts on weekends, so I don't even get home untill the next day. Her sheets get washed as soon as I get home, but the problem is that it has gotten so far into the mattress I can't get it out. We have tried baking soda and vinager. It got rid of the overwhelming smell when you walked into the room, but I put my hand on her bed and my hand reeked like urine. I'm looking for a new mattress that we can afford but does anyone have any ideas untill we find one?