Lots of deer are killed every year in these woods with a 20 gauge shotgun. You've simply got to know the limitations of your firearm. Buy some 5-packs of buckshot from a couple of manufacturers and pattern them at a convenient range. Use the one that patterns best.
Our shotguns like Federal buckshot. It comes in several varieties, the 2.75 load is 20 pellets of 3 buck and the 3" load is 18 pellets of 2 buck. Try them both and use the one that patterns best in your shotgun, then go have fun.