I wear an overnight-capacity hourglass-shaped disposable anatomic pad (such as a Moliform Super Plus or an Abena Abri-San 11) to bed. Those are the highest capacity, most absorbent product I have found. I keep the pad in place with a cotton-spandex stretch pant (such as the Abri-Fix cotton pants — sort of a spandex granny-panty). The stretch pant also keeps the pad snug against my body, which seems to help prevent flooding out.
The pad is essentially a super-absorbent, super-capacity brief, without the side plastic and tapes. I used to wear the corresponding briefs. When I first changed to wearing the pad, I was afraid the pad would leak, but I discovered that if a pad would leak, so would a brief. The pad holds as much as the brief, and the side plastic on the brief doesn’t absorb anything. The pad is also easier to put on, change and take off — and it’s cheaper.
I put a waterproof-backed cotton bed pad between the sheet and the mattress pad to catch any leaks. Putting it under the sheet keeps it from bunching up or sliding out of place, although it does mean that any leaks wet the sheet. The bed pad has caught every leak from the pad, so I no longer put a plastic sheet under the mattress cover.
Most nights, the anatomic pad absorbs everything. I wake up some mornings with a damp stretch pant. The sheet will have a spot once or twice a month.
A few times a year, I wake up in a puddle. I change into a dry pad and pajamas, lay another waterproof bed pad over the wet spot and go back to sleep.