I ordered some called Snuggease. They are reusable. I got them to assist Holly with potty training, a reminder at night not to go in bed. She peed in them once and got the message. Has not peed the bed since. They are washable, very absorbent and fit great. I tried the disposable diapers and they fell off before morning. These fit great. Here is a link to where I ordered them from:
Dog Diapers | SnuggEase Protective Pants for Dogs