Hi James,
Throughout my childhood and teenage years, I had a toy poodle who also had diabetes. She was diagnosed at the age of 6, along with cushings syndrome, and lived until she was well in her teens.
Back in the 90's there wasn't a lot of advice given, so we managed her diabetes through trial and error. Every morning we would catch her first wee of the day (using a little saucer that we'd run out and put underneath her just as she'd started to wee), and would test using the keto diastix (available from the chemist). This would always give us a basic idea of where her levels were and how much insulin to give her.
Food-wise, we were duped by the vets into the idea that you must feed specialist canned food - back then it was called canine WD and looked a lot like compressed sawdust. In later life, she turned her nose up, so did pretty okay on a diet of boiled lean meat, fish and veggies.
There were moments when she went a little wobbly - and if this was the case, we would go by what her morning diastix said... if her levels were high we would give her an extra couple of units and a longer walk, or if she was too low, she'd get a treat - usually a corner of toast with the tiniest smear of jam on it.
Being diabetic now myself, the advice for humans is pretty much the same as the trial and error way we learned to control our dog's diabetes... low carb diet, regular exercise, and routine monitoring.
Good luck!