1. A Kansas Soldier at War: The Civil War Letters of Christian and Elise Dubach Isely by Ken Spurgeon (The History Pr, 2013).
This is a welcome study of a soldier who served in the Trans-Mississippi with the 2nd Kansas Cavalry. Isely's letters to his wife are not reproduced in full but rather as excerpts integrated into a narrative. I am not yet sure if arrangements have been made to make the full letter transcriptions available online.
2. Guerrilla Hunters in Civil War Missouri by James W. Erwin (The History Pr, 2013).
Rather than a high level overview of the counterinsurgency campaign in Missouri (though there are probably elements present), this book appears to concern itself instead with geographically representative individual accounts.