I have this one: Uniquely You and it's great. Better than the cheap adjustable ones. I've also very much admired this one: Fabulous Fit and have been eyeballing it since I'm not quite the same size I was when I bought the Uniquely You one.
You buy a dress form that is two sizes smaller and build it up with batting. It is a lengthy process.
http://blog.gorgeousfabrics.com/2012/09/22/getting-close-on-the-dress-form-double/
http://blog.gorgeousfabrics.com/2012/06/17/final-muslin-for-the-body-double/
A shortcut is to use the Fabulous Fit system, along with additional batting.
Someone did this for me using the Fabulous Fit system and covers. It took about seven hours. The traditional method can take at least 30.
Quality forms include Wolf, Superior, and Royal. You can sometimes find them used on Craigslist.