Body doubles during sex scenes are most commonly offered to actors when a specific part of their bodies are asked to be shown on camera, such as breasts or asses.
The fact that Sebastian was offered one but chose to do the entire thing himself gives me good reason to believe that we’re finally gonna see his badokadonk in all its glory.
On my tombstone, please make sure to engrave the following:
“Swiggity swooty, death by SebStan’s booty.”