Seeking a good mattress pad

Our daughter just turned three and has been potty-trained for about 2 and a half months. She would wear pull-ups at night, but for the past week has refused to wear them. To her credit, she is hardly ever wet in the morning, but there have been occasions. So instead of fighting about the pull-ups, we want to find a good pad to protect the mattress that is not incredibly bulky but that is large enough to not shift. We're also having a second baby in January, so I figure this will come in handy then when the diapers leak. We used to put a crib protector sheet under the baby but it migrated all over the place and drove me nuts.