Several things help with a creamy mouthfeel.
More malto dextrins/residual sugars
Assuming you don't have the capability of serving the stout from a keg on Nitrogen some things you can do.
Reduce your hops addition and eliminate the late additions
Use less sugar for carbonation.
Increase your mash temp, flaked oats and/or crystal malt
My smooth oatmeal stout is quite creamy but the biggest key is keeping the carbonation fairly low. At normal carbonation levels the CO2 provides a bite.