Mark,
I think a good place to start would be with Allen Guelzo's "
Abraham Lincoln and the Doctrine of Necessity" which was published by the
Journal of the Abraham Lincoln Association in 1997.
I don't think Lincoln thought twice about his personal safety for a myriad number of reasons, but first and foremost (at least in my mind) is that no one ever seriously considered that assassinating a president would ever happen in America, even in an occupied city. Plus, ala Guelzo, if Lincoln thought seriously that his life would ever be in danger, there would be little he could do to forestall such an action.
By the way, welcome to the forum.
Best
Rob