Visting Khara Khoto (Heicheng) and Badain Jaran Desert (Badajilin Shamo)?

Hi,

How can I best visit Khara Khoto (Heicheng) and Badain Jaran Desert (Badajilin Shamo)?

I understand I need permits to visit? Can I visit alone or must I book a tour with an agency?

Can you recommend an agency based in Hohhot? Preferably in English but Chinese is ok.

Thanks!