Recs if you like The Origin of the Family Private Property and the State: Frederick Engels...

The leftcom perspective: the line running from Marx to Lenin, to the foundation of the Third International and the birth of the Communist Party in Livorno, 1921. The struggle against Stalinism and the degeneration of the revolution in Moscow.

Missing a lot of important articles by virtue of them not being books. Google "ultraleft new reading list" for the whole thing

I like history so I also added some Marxist-adjacent history works that (I think) are a good complement to all the theory here