@Purdey welcome to the forum. Some of the choices depend on your medication, whether you need to lose weight and tastes. I was diagnosed a year ago and haven't eaten porridge since. I have a BG monitor and will when it is colder try. porridge again. What I usually have for breakfast is full fat Greek style yoghurt. My favourite is from M and S but it is personal taste. I have it with raspberry strawberry or blueberry. I noticed my local cafe adds a dollop of peanut butter which makes it more filling. Last year I used to pick blackberries a 5 minute walk from my house but they were dug up in spring. Some people add a spoonfull of granola. I adda few nuts either almond, hazelnut or walnut and sometimes seeds. You can buy them easily. Other times I have a mushroom omlette. This morning I had a couple of hard boiled eggs. I had half a dozen which were a bit old. I cooked them in airfryer dunked in cold water peeled and put in the fridge.
Once a week I have a fry up without hash brown or beans. I have a slice of bread a few times a week.