Hi,
My little girl was only recently diagnosed type 1, so I am not sure if I am qualified to give advice as such. I can only tell you what the diabetes nurse advised us, and so far this seems to work for her. Everyone is different though.
We give her normal low fat, high fibre meals, but each one will have (slow release) carbs in. Usually about 40-55g per meal. But she's only little (8), your son with his busy job might need more? I dunno. Slow release carbs will convert to glucose slowly, keeping blood sugars steadier than fast release carbs (simple sugars in fizzy drinks/sweets etc). A typical breakfast for my girl would be 2 weetabix with semi-skimmed milk (no sugar added), with perhaps a few raisins. Or porridge with grated apple and cinnamon to sweeten. Lunch, wholemeal bread/ pitta/wrap, some fruit, a low-sugar yoghurt. Dinner might be a jacket potato with baked beans and cheese or tuna pasta bake with a salad. If my girl is really hungry but her blood sugars are a little on the high side, I might give her more protein with her meals or snacks (fish/meat/cheese/eggs) as proteins won't affect her blood sugar. She gets small slow-release snacks in between meals to give her glucose levels steady. 15g carbs in each (so maybe 2 small oat biscuits, a bag of snack-a-jacks, some grapes).
I think your son needs a lot of support from his diabetes team, perhaps a visit to the dietician, have another look at his insuline regime etc. I hope it gets sorted soon, sounds really difficult for you. Best of luck.