how much lactose

I have never used lactose before but I have an oatmeal chocolate stout that I want to sweeten a bit. The chocolate is a little bitter and I think a little sweetening and body would really make this good. It is still in primary and I am heading to the brew shop tomorrow. SO for a 5 gallon batch what is a good starting point with ther lactose.. I know I should have added it to the boil but too late now lol...any suggestions or ideas would be appreciated.

It really doesn't add any sweetness more of a mouthful feel or body. But I use it in my stout recipe. 1 lbs per 5 gallon.