There is a non-nude site close to Studland and a nude one a little farther away I think?
For my own research I just used maps such as multimap to find out of the way places. Common sense tells you when you are far enough away from prying eyes to go nude and enjoy it. It also means you avoid the crowds if you want to have fun.
Following that it is possible to find campsites nearby. If you want naturist campsites a Google search will pull out the main ones quickly enough. Try the Uk camp site for general campsites. Sorry, URLs not allowed