If you're interested in SS involvement in the camps system in particular, the first volume of the USHMM Encyclopedia of Camps & Ghettos is mostly focused on this.
There's a relatively short introduction
available online to that section of the encyclopedia.
A much longer history is Wachsmann's
book KL - A History of the Nazi Concentration Camps. Looks like an epub version is available from the usual suspects. It's written in a more popular (versus scholarly) style.
They're mainstream works, but Thomas Kues and John Wear have cited Wachsmann's books on the concentration camps in articles on CODOH.
I often like reading journal articles more than books, because they're shorter and more focused. For particular topics on the SS you're interested in, Google Scholar will bring up a good number of books, articles, and theses/dissertations. Many are open access, and if they're not, they're often available from the usual suspects.