I make my porridge with 30g porridge oats, water and salt. Once cooked I top it with fresh fruit (usually raspberries or blueberries) and a splash of milk.
Porridge itself is low in sugar, salt and fat, it's the stuff that's added to give it flavour that adds calories.
My method: 4 heaped tbsp of Jumbo porridge oats, soaked in water over night, then add enough water so it swishes in the pan, a sprinkle of salt. Bring to the boil, low simmer for 5 minutes, stirring. Pour into a bowl and leave for a couple of minutes. a little sugar and cover with cold semi milk.
You could try overnight oats.
In a bowl or a jar, layer jumbo oats with plain Greek yogurt, a handful of berries, and maybe a sprinkling of toasted seeds or nuts. Cover, leave overnight, stir and eat in the morning.
You can add a sprinkling of cinnamon, cocoa powder, or a bit of vanilla extract too.