While Nazis were dedicated anti-semites, but they were opportunist anti-slavs.
Croats, Bulgarians, Slovaks and Cossacks were treated okay, because they were useful. Czechs gave up without fight, so were treated less bad than Poles. Russians and Poles resisted, so were brutalized second only to Jews, gypsies and likes.
All you need to do is to convince top nazis that Poles, Belorussians, Ukrainians and Russians were more useful alive. Have them make excuse that Russian pre-communist elites are half-Varangians descended from vikings, half Baltic Germans descended from Teutons (its half truth. Baltic Germans were considerable part of Russian aristocracy), and you have convenient group that hates USSR to form backbone of collaborative regimes found among white emigre and political prisoners rescued from gulags and prisons. (Not that crazy. Germans were arbitrarily designating members of collaborative Russian Liberation Army as non-slav cossacks, a complete nonsense, but this way they keep illusion of obeying their racial superiority ideology. Guess what, Nazis were hypocrites on top of everything else. Huh, who would have though). Have nazi propaganda aimed to ethnic Russians, blaming jews for Soviet repression.
There is still large amount of suffering on eastern front, since even without explicit Hunger plan aimed at genociding slavs, civilians get caught between Wehrmacht and Red Army, but its behaviour toward non-jews will be more like behavior of World War one wehrmacht, than its OTL counterpart.
If you twist the idea of "lebensraum" to mean indirect exploitation, not direct slavery, you will still get Barbarossa, but with goal of creating puppet states to be economically, politically, and militarily tied to Germany as they were in 1918 after Brest Litovsk, and not making everything between Germany and Ural a slave camp. In instead of Reichkommisariats, Germans would set up "Democratic Republic of Ukraine", "Free State of Belarus", "Sovereign Principality of Rostov", etc. (names are lies, if you are sarcasm-blind)
Nazis still commit holocaust (not nazi enough to count as nazism?) but are more likely to use local puppets to do dirty work for them, still have goal of conquering large territory, still cause untold amount of suffering, its just one (admittingly large) group that manages to not get as screwed as bad it did IRL.
Survival of Max Erwin von Scheubner-Richter sounds like a good POD, he would be Russian lobbyist in Berlin, ensuring Nazi policy in the east will be softer than IRL.