The Secret to Co-Sleeping With an Infant...
...is to double up on the mattress pads:
We use the standard fitted pad that covers the whole mattress, as well as a smaller one that can be yanked off in the event of a Diaper Malfunction. This allows us to change the sheet and fall back asleep quickly, skipping the "What if he does it again and soils the mattress?" conundrum that haunts the waking nightmares of sleep-deprived parents.
The trick is to position the smaller pad in such a way that it covers both the Spitting Up End and the Peeing Out Of His Diaper End.