Add some good (low sugar and low added fats) peanut butter or any other nut butter and/or ground nuts to your oats. Makes for a healthy and calorie rich meal that keeps you sated for a while. It’s easy on the stomach, does not cause the blood sugar to rise quickly and you can eat it spoon by spoon over the whole day, if necessary.
Also don’t forget to drink plenty. I find tea and highly diluted apple juice (like 10%) are ideal when I am sick.