IMO, the best thing to do in this regard is read what is cited in the footnotes of the Vatican II documents.
The CCC is also a good source for this. The different Councils and papal documents are often dealing with different aspects of a topic, and the CCC can present the coherent whole on the topic, citing the different sources which which shed light on each aspect.
For example, some claim Dignitatis Humanae contradicts the encyclical Quanta Cura of Bl. Pius IX, but there’re really just dealing with two different aspects of the Church’s doctrine on this topic. In the Catechism section on religious liberty (2104-2109), Dignitatis Humanae is cited for some paragraphs, but Quanta Cura is cited as the basis of par. 2109. Reading the whole section together, one can see how the teaching of each document fits coherently as part of the Church’s whole doctrine on religious liberty.
Also, for a specific example off the top of my head, in his encyclical Ecclasiam Suam, when speaking about the Council’s work in Lumen Gentium, Pope Paul VI specifically pointed to the encyclicals Satis Cognitum of Leo XIII and Mystici Corporis of Pius XII as especially important to consult.
