Besides Foote's trilogy, this is one I'm going to get. Anymore I'm about 3 or 4 books behind on a regular basis so I think with those that'll put me about 7 or 8 behind. :)
Foote’s trilogy in soft-cover is the way to go. It’s considerably less expensive than the hard-cover version. My McPherson copy is also soft-cover.
If anything, these two historical references will give you all the knowledge you need for a good, in-depth understanding of the times and the conflict.
And don’t worry about being behind. Reading is something you can never catch up on. There’s always more... :)