I've read posts and suggestions for how to handle over-night potty issues while potty training little ones. One person suggested layering the bed with a plastic sheet, then a cloth sheet, then plastic then cloth... then you could take one layer off at a time (even overnight) if you needed to. If it comes to that, I'll try that!!
But for me, what works for now is to put those plastic covered portable diaper pads under her sheet. (you know those that you got to lay your baby on when you go out)... I lay 2 of those in the spot where Lil M sleeps, under the sheet. If she moved around more, I'd put more under the sheet. Thankfully, she doesn't. :) Since I have a few of those pads, and they seem to work just as well as if i had bought some type of plastic sheet for the bed, that's what we use! :) And they're a bit cushy too...
Then, in the morning, I take the sheet off and wipe the plastic diaper pads off with Lysol and remake the bed.
We are not currently using pull-ups or diapers at night. I did put plastic pants on her last night... that helps a bit, too. :)