Westlaw (https://lawschool.thomsonreuters.com/) contains many treatises on contracts. Too many to list here! Once you're logged into Westlaw you have a few options to find these treatises - use the one search box to search for contracts, browse secondary sources, browse your jurisdiction to see if there is a specific contract resource, or see the titles on the left side of a search.
A prominent title, consisting of thousands of pages, is Williston on Contracts. The excerpt below probably matches at least some of your Contracts syllabus. Each section is huge! For example, just the introductory section on "offers" runs to 36 pages. There will be plenty of details as well as footnotes linking to cases. Remember, the market for this resource is attorneys not law students.
LexisNexis (lexisnexis.com/lawshcool) is the other great resource for treatises. While the methods on the left for finding West treatises hold true for finding Lexis treaties, there is also the option to browse by practice area on Lexis. Unlike in West, Contracts is an option on LexisNexis. Here is a snippet of what is available on Lexis:
