I have searched this site and have found several references to homemade diapers, but have not seen my particular application. If there is already a thread on this subject, my sincere apologies.
In spite of the best diapers (Bellissimo, Dry 24/7) we have all experienced leaks ("it" happens). Rather than modify the bedding for this problem, why not use a cheap "secondary containment" in the form of an "over-diaper" using a kitchen garbage bag and a pad of paper towels?
To partially plagiarize Bean from another thread "Unfold the the bag, cut off the bottom corners of the bag to create holes that are slightly smaller than the diameter of your thigh. Carefully put your feet through the holes and slowly pull the bag up over your legs slowly stretching the leg holes so they will be snug around your upper thighs." Then insert a pad of paper towels between the bag and the diaper.
What's good about the kitchen garbage bag over-diaper is that it is cheap, disposable, will fit over any size diaper, the bag leg holes are located not near the diaper leg holes so that there is no transference, it is soft and comfortable, and can ride as high as your chest if you want it to.