Marian,
John has already given some good suggestions regarding books on this topic, or that contain information on this topic. I would also like to mention that Bill Wormstedt, Kent Layton and my book "On A Sea of Glass, The Life & Loss of RMS Titanic", which is due out very shortly, goes into a fair amount of detail about some of the steerage passengers, and follows the story of numerous individuals from Third Class, as well as the crew and other classes, throughout the voyage and aftermath. Good luck with your research!
John, you are absolutely correct about "Centennial Reappraisal." In addition to information mixed in throughout, George Behe and Cathy Akers-Jordan have a highly detailed appendix that analyzes the accounts of steerage passengers, and the obstacles and challenges they faced in reaching the boats. The conclusions they reach are surprising, and refute some myths, while confirming other stories.
Kind regards,
Tad