There are plenty of headshot damage mods already out there. Most are optional files linked to larger mods, or are already incorporated into larger overhauls. Making headshots "realistic" is kinda subjective, since your headshot damage depends on weapon damage scaling. Downscaled weapons require a higher headshot multiplier, whereas weapon damage upscaling would be lower.

"Modular Arrow Bolt and Shot Damage", on Nexus, which doubles headshot damage might be for you.