How to make playing historical USSR more difficult? (SP)

I already play intentionally sub-optimal by focusing a lot of historical designs and division templates, building industry in my western states, building mils “too early,” purging the hell out of the army, etc. I get that the main limiting factor here is the incompetency of the ai, but even the expert ai mod doesn’t do it for me anymore.

I’d like to recreate the historical ‘flow’ of the eastern front (nearly get pushed back to Moscow, hold them at Stalingrad, then push back to Berlin) but I can’t seem to get the Germans strong enough to do that without me literally just abandoning entire states.

I know multiplayer presents a whole other set of challenges but I’d rather not deal with some of the cons of multiplayer.

Does anyone else have any methods for making the SP experience more challenging when playing a major power like the Soviets?