If you're looking for a party to replace the NSDAP ITTL, think about what party Gregor Strasser might have joined.
Why ?
'Cause seemingly he was the only political head of the time, who reflected about the successes and differences of the political parties of his time on the fight for the vote of the masses.
And the most successfull in that respect was ... the SPD (I render Spartakists, USPD, KPD as the offsprings of the SPD they were.)
His conclusion : ORGANIZATION
The SPD was virually the only political party in the Weimar Republic, that had an organization with countrywide division and subdivisions for members, personel, functions, themes and ... money, a political and personel administration, that no other party had at all and an administration for electioneering. They had professional politicians for that.
In a way due to the economical state of their followers and members they needed to develop such a system during the Laiserreich. Only with such a system people NOT being rich enough to 'play' politician could become members of the i.e. Reichstag.
All other parties, including the DNVP, still worked as a 'notables' party, more like a ... club of independant guys more or less similar goals and attitudes with enough money and time to care about politics.
Unfortunatly also with much less of 'party-' or 'fractionary-'discipline.