Can't help with a specific recipe, but I did a kit oatmeal stout as my first.
The smoothness I detected came with time: more than 2months in the bottle.
The oatmeal is supposed to add mouth feel, but I am too noob to notice. If you brewed one now, based on a recipe or two in the database, it will probably be really good sometime around fall.
I wasn't able to make mine last that long
