There are many routes you can go. If you want technical ones I suggest "The Cremation Ovens of Auschwitz", "The Rudolf Report" "Open Air Incinerations" and "Air Photo Evidence." If you want ones that analyze and cross reference witness statements and examine documents I suggest any Mattogno/Graf book on one particular camp. The MGK book "Extermination Camps of Aktion Reinhardt" updates fresh 'rebuttals' to their books "Belzec" "Sobibor" and "Treblinka" as seen
here. The new 2015 edition "The Real Case for Auschwitz" looks good but it is mainly a response to Van Pelt and Pressac's errors in the context of the arguments advanced during the Irving-LIpstadt trial in England years ago.
If you want more encompassing ones that touch a little bit on each aspect, technical and non technical, you should get "Dissecting the Holocaust" "Debating the Holocaust" "Lectures on the Holocaust" and "The Hoax of the 20th century." If you want more specialized studies not counting books focused on one camp, you may try Mattogno's "The Bunkers of Auschwitz" "The Central Construction Office of the Waffen SS (2015 edtion) or "Special Treatment: Origin and Meaning of a Term."
By the way, I hope you are at least knowledgeable enough to know that the holocaust handbook series was started because Germar Rudolf's work with Theses and Dissertations Press was put on hold while he was in jail. Michael took over TandD and only put out one book. The first edition of Dalton's book. He was criticized for not doing enough by some people. TandD fell by the wayside and Barnes in America picked up some of the Holocaust Handbooks series to put out newer version of the old TandD books that look like this. However, if you can pick up a classic TandD version of a Barnes book that is merely a reprint of an old TandD book, why not? They are very colourful and would be a nice addition to one's library. Example:
viewtopic.php?f=2&t=8276
But now the Barnes Review carries the holocaust handbook series and with updated third editions of certain titles, covers now look like this.

By the way, I recommend this recent post of mine in UPCOMING HOLOCAUST HANDBOOKS.
viewtopic.php?p=74400#p74400