Looking for recommendations on the history of the GDR

I want to ask you all for some reading recommendations on the history of the GDR. This is for a party thing I'm doing, so I'm looking for something credible that's not just anti-communist propaganda (and also not just apologia, but that's less of an issue obviously). I've heard that the PDS published a whole book series, but I'm having trouble finding it. Can anyone point me at some books or texts? I kind of have no idea where to start, so basically I'm just looking for a general overview. Thanks!