Instead, try and read more Holocaust Survivor memoirs. They tell the stories we need to remember and pass on when they are gone. It is our duty to make sure their memories are never lost; not the stories of a fictional child that could have never talked with or snuck into a camp.
Night by Elie Wiesel is always a great book. All But My Life by Gerda Weissmann Klein. And my favorite book of all time, Rena's Promise: A Story of Sisters in Auschwitz by Rena Kornreich Gelissen. There are plenty more you can check out at your library or bookstore.
Historical fiction novels are just that. They may have interesting and moving plots, but they aren't the most reliable in telling the entire story.
The actual Auschwitz Museum has made many statements on the books' credibility or lack thereof.
You should never base your information on an event so heavy as the Holocaust on a fiction novel. They can spread false info, and with a period in our history that already is under so much controversy, we simply cannot allow it.
Here is another article that tells the true story behind the Tattooist of Auschwitz as well as discussed the importance of fact-checking historical fiction. It is not to say that these books aren't good books. The fact that they have so much popularity is a good thing; it means that readers are at least taking an interest in the Holocaust. However, reading them does not mean you have just absorbed a crash-course on the Holocaust, or any historical event for that matter. Historica; fiction novels should be used as a gateway read into reading non-fiction texts, such as memoirs or primary sources.
While a book may be "based on true events" or "based on real people," it doesn't necessarily mean it's the entire truth or even the truth at all.