Here is an article which references primary sources:

The facts in The War Behind Me were drawn from a declassified Army Staff archive of reports on U.S. atrocities, and from interviews with the Pentagon officials who compiled the records and combat veterans named in them. - See more at: http://www.crimesofwar.org/commentary/the-war-behind-me-vietnam-veterans-confront-the-truth-about-us-war-crimes-in-vietnam/#sthash.bsgUDniY.dpuf

http://www.historynet.com/interview-larry-colburn-why-my-lai-hugh-thompson-matter.htm

https://archive.org/details/InterviewWithHughThompson-AmericanHeroWhoStoppedMyLaiMassacremp3

http://www.npr.org/templates/story/story.php?storyId=5133444

I took a 4000 level undergrad class on Vietnam, and we spent an entire section on My Lai. Probably the most comprehensive collection of testimonials and primary sources is this book, My Lai: A Brief History with Documents by James Olsen and Randy Roberts.

I highly recommend this book. I'd say it is exactly what you are looking for