Assuming you have regular/plain porridge oats then it's fine to give him those (and I'd choose that over baby rice which has little nutritional value). I wouldn't suggest using any of the flavoured oats which are available off the shelf due to added sugar and salt. The quick oats such as Ready Brek Original are fortified so there are a range of extra vitamins added, you might consider those if they are available where you live (again the flavoured packs have sugar added so I'd avoid those for a young baby).
It's fine to offer him the regular oats but if you would be happier to begin with a smoother mix you can whizz the oats when they are dry which will make a much finer porridge.
There are also a few recipes for finger foods made with oats, porridge fingers, oaty chews or oat biscuits (sugar and honey free) or oat muffins if you want more finger food ideas.
You can also soak oats overnight in milk which makes them nice and soft, rather than cooking them into porridge which might be easier when making a very small amount.
It's ok to use cows milk in preparing foods but obviously breast milk has more nutrients for baby and tastes sweeter too.
hope this helps