The thickest period pads are going to be either the Always Maxi Size 5 or 6 (they're almost exactly the same size) or the Kotex Maxi Extra Heavy Overnight. The Always size 5 are the least comfortable of the three, and I use actually these for "period week" for that reason. They're usually the cheapest and who ever said periods were supposed to be comfortable
The thickest incontinence pads are going to be the tena or poise overnight pads. I wear them "backwards" with the wider section up front and they seen to fit perfectly. I usually go with Poise just because the plastic backing is a really nice lavender color and thats kinda my jam.