Cat diabetes diet

My cat is 14 and newly diagnosed with diabetes. I'm looking to supplement the insulin shots with a better diet. I don't want to cut out canned food because he loves it. My vet said he had a dry food that would help but I would have to cut out the canned food (friskies) because it would contradict what good the dry food would do.
I understand something like Wellness canned food would be good, but is it good for diabetes and would it not work with the diabetic dry food? I'd like to let him eat both, like he does now.
He also takes medication for hyperthyroidism. I'm worried about him continuing to lose weight. He's at 13.5 lbs now. But he was heavier.