Are you asking for sims 4? There has been tons of nude mods by now. You can either:
1. Set nude as clothing using Snaitf's Nudists mod
http://sexysims.info/download.php?t=174690. This is the basic way.
1.1 You can also search for various naked skins for your sims, beside the basic EA skins. I suggest you dig sexysims for more of these, or do a quick google search. Sadly, many of tumblr modders's posts have been blocked after the tumblr cultural revolution earlier this month so I can't point you there.
2. Why use nude clothing anymore when you have Wicked Whims
https://wickedwhimsmod.com/. I find this better, more realistic and less annoying. You can have your sims wearing their clothes and have them undress any time! Wicked Whims also adds the nudist and exhibitionist traits. You start with only undressing in your room, then your house in front of other sims in your family, then in public. Wicked Whims has other adult aspect with sex and exhibitionism, but you can use it or disable it, it doesn't matter. You can set the pregnancy setting, female sims's menstrual cycles.
Check their website for the skins as well! Genitals look very realistic. You can add realistic pubic hair as well!
Of course you can still have you sims wearing glasses, hat or shoes, or accessories.
Check out some of my sims below. With a variety of skins you can have very diverse body types, genital shapes, and even nipple shapes and colours! The penis size and shapes are less diversified so I'm still waiting for the modders. I know nothing about modding, I'm just a collector haha.
In CAS:
In game (these were old images, before Wicked Whims and some of the new skins):