T.W.
LOL, a common issue it seems. I used to untie one side (the short side (two ties) of the bumper, slip the mattress out of the crib completely and then slide it back in and retie the two ties. Luckily I never had an issue with spit up or wetting through diapers and he always napped somewhere else so I didn't have once a week at the most.
I can't say as I have had to change my 8.5 months olds crib sheets ever since HE WON'T sleep in it!
Good luck, it doesn't last forever, next it will be the toddler bed or the big kid bed, which is just more sheet to wrestle with!