Well, first of all are you brewing extract with steeping grains, partial mash, or all grain? If you're doing extract and steeping grains, I don't think oats will do much for you. But either flaked oats from a home brew supply store or regular rolled oats from the store can work. Just make sure it's organic rolled oats or "old fashioned" oats, not something like quick/instant oatmeal.
You cannot get all the goodness from oats without mashing but you can still get some of it by steeping. You can either use quick oats where the manufacturer has processed them using rollers and heat to gelatainize them or old fashioned oats can be cooked first and then steeped. Oats should give you a smoother mouthfeel and better head retention.
You can steep the oats or flaked barley along with other specialty grains in an extract+steep brew. You will get a little flavor, but the real goal is the creamy mouthfeel that you get from the flaked grain... and that will be there. I tend to go with one pound of wither flaked barley or oatmeal whether I am steeping or doing an AG
As a warning, I did my first Oatmeal Stout about a month ago and it was the most active fermentation I've experienced by a mile. I put about 5 1/4 gallons of wort in a 6.5 gallon carboy, no starter and within 12 hours it was spewing from my airlock. A blowoff fixed the problem, but be prepared. Oddly, the kit from my LBHS is called Up and Over Oatmeal Stout..I see where the name came from!
6.5 gallon carboy seemed to be plenty. The krausen never exceeded 4 in. I steeped the rolled oats in it's own bag, changed the color to a thick brown rather than black. Looks like it'll be a meal in a glass. Haha.
I'm thinking something along the lines of a Boddington's. Most of my experience drinking it is from the widgeted cans, so I'm thinking a smoother mouthfeel might get that feeling a little? I'm a straight kit and kilo extract brewer at this point, I don't want to get too far away from that, at this point anyway.