You can look at Flintlock as well. Has good level sites, but is pretty close to the main road, and has a pretty good hill at the entrance / exit.
Also there is Boone KOA. But the sites are not real level.
While not exactly in Boone. Raccoone Holller CG is one of the best in the area. It is in Glendale Springs, just over the mountain.
We also like Honey Bear. But there are only about 4 campsites that we would consider staying in, and those are always full.
Terry & Shay
Coachman Apex 288BH.
2013 F150 XLT Off Road
5.0, 3.73
Lazy Campers