I'm not sure that any such account exists, I've certainly never heard of one. But many personal stories are available from people who survived the death camps. You can find some of them at this link.
The most powerful thing I've ever read about the Nazi camps was a poem written by Yevgeny Yevtushenko. He gets down to the very soul of the camps and manages to capture the despair of the victims. It's very moving. It's called The Light Controller and, although it's not published anywhere on the Internet, I once copied it for a friend on Ask. You can check it out on my Dropbox page: HERE.
I wish you well with the story. I'd love to read it if you manage to get it finished.
