I'm not sure which platform you're on, but certainly there's a mod for PC - hope this helps.
http://www.nexusmods.com/fallout4/mods/522/?
On the Playstation 4, no modding available just the plain old vanilla experience. Thanks for the response, now I just hope the developers see this thread and are like "Hey, what a great idea!" Then just pop out the back and press a few buttons and KABLAMO all done and dusted. Well, that is the dream we all have posting on here I guess lol
At this stage of the game, I wouldn't trust any mod with an esp. Until the GECK is released (or whatever Beth chooses to call it) it's probably best to forego mods until proper tools can be used.
As for lower guns in first person goes, I get the desire for that, but in my experience, when I aim down the sights of my guns (handguns or shotgun) my focus is on the front sight. Everything beyond the end of my gun is a blur, as it should be. Certainly there's more to shooting than that, but for aiming down the sights in game, I've got no issues with it. I've got issues with other aspects of Fallout 4, but that'd be off topic.