Linked above is the UofT research guide to Vatican II. It is a great start for beginning diving into the vast and deep topic which is an ecumenical council. The guide contains concordances, commentaries, speeches and debates and contempory accounts.
Unfortunately several of the works are hard to find unless you have access to a theological library.
I would like to add a new concordance recently published (even if not from an established publisher) to the list available online because most of the ones listed in the guide you can’t purchase as they are out of print. See here.
I also believe that Renewal Within Tradition by Mathew Lamb and Matthew Levering should be included on any guide to Vatican II.
If you are looking for free material that does the trick, check our this website’s links and resources page. https://defendingvatican2.ca/defending-vatican-ii/4-0-links-and-resources/