time for a new mattress

My daughter Haileys Mattress had a little cut in the plastic cover since i can remember, it never bothered her so i didn't really think about replacing it. Well i put her down for bed and a few minutes later i heard her giggle in her room, and some weird ''scratching'' noise... i went into her room to find her sitting on her bed with bits and pieces of her mattress all around her LOL... she ripped the plastic cover open and started to pull out the foam and cardboard from the inside!. little stinker! i guess ill have to go shopping soon! She needs a new bed anyway hers was given to use and THEY used for quite some time before we got it! i want one that you can convert into a toddler bed.