Berger is highly technical, not much of an introduction.

On Bayesian statistics, Bayesian Data Analaysis is a classic.

"Bayesian decision theory" usually just means "normal decision theory," so you could start with my FAQ. Though when decision theory is taught from a statistics book rather than an economic book, they use slightly different terminology, e.g. they set things up with a loss function rather than a utility function. For an intro to decision theory from the Bayesian statistics angle, Introduction to Statistical Decision Theory is pretty thorough, and more accessible than Berger.