Literature on the First Avar Khaganate in English is probably the problem you're having. They're mainly in German, Serb, Hungarian, Romanian, or Bulgarian. Overwhelmingly in German, though.

Pohl's Die Awaren is the basic reading, and is in German. I know of no comprehensive English works on the Avars. We have few enough on the Huns (despite the fact the Avars are far better attested).

There are some collected works which include papers on the Avars, such as The Other Europe in the Middle Ages, and Avars, Bulgars, and Magyars on the Middle and Lower Danube. However they tend to cover specific aspects as academic papers and are not comprehensive histories. (Also the second one is Hungarian and well... there's a lot of nationalistic pseudohistorical bias that infiltrates these topics, and I recognize one of the editors as one of those hyper-nationalists that doesn't understand Etymology and claims the Huns were Hungarians).

In English*, sorry