You might misunderstand what Fraenkel means with "Dual State". That doesn't mean a "Nazi" and a "Non-Nazi State". Fraenkel work is dedicated to analyzing political and judical system of the Third Reich.

He differentiates between the "normative" and the "prerogative" states. The first refers to the old judicial bureacracy that was already established, including laws, the court system, public administration, contracts and private property. It guaranteed, among other things, the continued function of the capitalistic economic system.

The prerogative state did not abide to the rule of law. This included the government, the party, Gestapo and other Nazi institutions. In their decisions and actions, politicial considerations took precedence over Rights and laws. The following is quoted from Frankel, but I'm no English Major, so take the English translations parts with a grain of salt:

The "prerogative" ("Maßnahmen") state makes decision based on "the current state of affairs" ("nach Lage der Sache"). In it "norms [rules] are missing and actions reign" ("fehlen die Normen und herrschen die Maßnahmen").

The pregorative state is based upon the Reichstagsbrandverordnung, a decree issued by then President Hindenburg in 1933, suspending parts of the Weimar constitution including key civil liberties. Fraenkel argues that the continuous state of emergency initiated by this decree effectively makes it the constitution of the Third Reich.

Sources:

Michael Wildt: Die Transformation des Ausnahmezustands

Edit:

Regarding your real question. As I'm German I can't guarantee the qualitiy of translations, but I can recommend Bernt Engelmann. He was "exceptionally successfull and controversial" but the "controversial" part mostly refers to his later works dealing wiht contemporary issues as he had associations to the East German author association (among other things that might have compromised his academic academy.)

He still wrote good books about the life ot the common folk under the NS tho and was a proponent of a more "bottom up" way of approaching history. You can look into his works.