Andy Naselli linked to this excellent bibliography by Phil Gons on Union with Christ.
We recently discussed this in our small groups (Chapter 3 of How Can I Change? by C.J. Mahaney and Robin Boisvert)
They referred to an excellent resource in their chapter, which was none other than D. Martyn Lloyd-Jones commentary on Romans 6 especially pp.106-148.
Enjoy and have a full soul after this great doctrinal truth settles upon you.