The High Bun.

The High bun, Top Knot or ballerina buns are making the rounds amongst celebrities as the hairstyle of the moment and it seems it is here to stay for awhile at least.
From messy, textured to full the high bun is as easy to make as any other Up Do hairstyle.
Tip: Pull your hair into a ponytail, twist the hair slightly and wrap it upward and around the elastic band for a fuller-looking bun. Secure it into place, and then smooth the top knot with your brush to tame any fly-away.

From L-R: Textured Bun, Sleek Bun, ,Messy Bun, Big Bun.

If your bun isn’t as thick as you want it to be, you can clip in a hair extension underneath a layer of your hair inbetween the crown and nape of your neck, but put it in upside down. So when you pull it up into a ponytail the clips that keep it in won’t bulge out due to being pulled in the opposite direction.
Remember that not all buns have to be professional looking. A messy one can easily do for a laid back look. And you can do one in braids ala Beyonce.