J.P.
If he refuses to go back to a pull-up, you could try waking him to go to the bathroom before you go to bed. That might give him enough relief to make it the rest of the night.
Here's a trick I learned for the sheets: Put on the fitted sheet. Put an absorbant underpad approximately where he would be wetting. Take a flat sheet folded in half and wrap it over the underpad, tucking it in. Then finish making the bed as usual. If he wets, you will (hopefully) only need to wash the one flat sheet and you won't have to remake the whole bed in the middle of the night.
Good luck,
J.