Nothing to Envy was great and so was Escape from Camp 14. I can recommend The Aquariumms of Pyongyang by Kang Chol-hwan and Pierre Rigoulot. The Kang family became prosperous in Japan in the 30's but returned to North Korea in the 60's, only to be sent to prison work camps. Tough topic, written well.
Edited to add: also good is The World is Bigger Now by Euna Lee or Somewhere On the Inside by Laura and Lisa Ling. Both Euna and Laura were held in detention in North Korea after filming there for National Geographic. I just saw the actual piece they filmed inside North Korea and it is full of footage in the country, if you can find it, definitely watch it. Its thrilling. I found it streaming online.