I don't know much about Armenian history if I'm honest, but 'Armenian Golgotha', a diary written by a priest who survives the Armenian genocide, was very interesting (especially with the added details about WW1 and the majority of religious beliefs). I also enjoyed (we'll not enjoyed, it's not exactly a cheerful topic) 'Black Garden: Armenia and Azerbaijan Through Peace and War' which gave me a real insight into the Nagorno-Karabakh war. That's all modern though, and doesn't give much of an insight into Armenia outside of conflicts.

Maybe the History of Armenia/of Lazar P'Arpec'i could be helpful? It was written at the end of the fifth century.