My daughter has the same problem occasionally. She uses cloth diapers in the day but I put her in a disposable at night because she wets so much. I put the Bummis Super Whisper Wrap that I use for her cloth diaper cover (available here http://www.bummis.com/en/Products/covers/SuperWhisperWrap.html ) over the disposable diaper to keep it from leaking through. They're made of super resistant waterproof laminate sandwiched between two layers of a soft polyester knit, so it's really soft on their skin unlike traditional plastic pants that my mom used over cloth diapers when we were kids. Plastic pants would work just as well, and are available in the baby department of any store - Target, Walmart, Etc.

Good luck!