My DS has always been a heavy wetter at night as well as a tummy sleeper so we've had issues with leaky diapers in the morning. My solution was to buy these booster pads on Amazon and line his nighttime diaper with it. It's not 100% leak proof, but it's 95% better.
Pull Ups Nightime/Overnights, Babies R Us own brand of training underwear (aka pull ups) and Earths Best Training Pants (aka pull ups) are the only ones that don't leak
Re: Recommend a nighttime pull up that won't leak!
https://www.amazon.com/Tranquility-TopLiner-Booster-Medium-Inserts/dp/B002DQY9HO/ref=sr_1_2?ie=UTF8&qid=1379015727&sr=8-2&keywords=booster+pads