The Book is entitled "When We Went First Class," by Ellen Douglas Williamson and published by the Iowa State University Press. Mrs. Williamson's father and Walter Douglas were brothers. The book basically chronicals the lives of Douglas family (primarily Mrs. Williamson and her two sisters) and the very privileged life style they led from the turn of the century onward. It isn't really a "Titanic" book per se; however, one chapter entitled "Traveling by Ship" chronicles her own experiences as a passenger on quite a number of different liners, with six pages devoted to the Titanic disaster and the death of her uncle. It isn't a very scholarly book, and her recollections contain some errors, but it is an intersting read. She writes with some detail about Mahala Douglas's experience on the lifeboat, and addresses the rather unsavory topic of the lack of chamber pots on the lifeboats in a rather humerous way.
The book can be purchased at Brucemore, a National Trust property in Cedar Rapids, Iowa, which was the home of the Douglas family. A Brucemore website can be found at both Brucemore.org and Brucemore.com. I don't know whether you can order the book directly online, but I know they have them in stock because I just purchased my copy recently.