https://www.january.ai/blog/oatmeal-alternatives
This article says that the least processed foodstuffs are bette for you, and that adding a few tsp of oat bran will really help to reduce the glycemic impact of your breakfast. The milk won't help if you add it since most of milk's calorific content comes from sugar. Berries, bananas, raisins, dates, even walnuts, will improve the meal (for some who enjoy adding things to oatmeal) but it will also likely raise the glycemic index.

Steel cut oats, if that's all the processing it has, is going to be somewhat better than rolled oats, especially if we're talking about the 'quick' or 'minute' oats with is almost pure carbohydrate. But it's still a grain, and grains have a hefty carb content.

I use whole oats (whole grain). I cook a batch in my pressure cooker. I add berries, chia seeds or basil seeds, freshly ground flax seed, dash of cinnamon etc., and soak in non-dairy milk. I stay away from honey for now since it is sugar. this combination is not fluctuating my blood sugar that much.