It won't give you specific advice on treatment, but to understand what the disease is, how the different treatments have developed and why advice is given in the way it is, you can't do better than Robert Tattersall's 'Diabetes: The Biography' (Oxford, 2009). Most of all, reading the horror stories of past treatments and medical ignorance should make all diabetics relieved that they have the condition now, rather than 50 (or even 25) years ago.