SJay, are you putting anything on your porridge, eg fruit, milk, cream, low-sugar jam etc?
Do you vary what you put on there? Coz that could be making a difference.
Also, how are you making it - are you varying how much milk you use ? Don't forget milk has carbs in. Are you using the same amount and kinds of oats? Some absorb more milk than others.
the only other thing that occurred to me is that 2 units of insulin for a bowl of porridge is pretty low - if you can get hypo on that I wonder if your body is still producing a little insulin of its own? That could be messing things around, especially if it is doing it intermittently. How recently were you diagnosed, could you be entering a 'honeymoon' period? (some type 1s have a short time where they actually come off insulin as their pancreases have a last gasp of life before packing it in.)