You can use any iteration of CAS to put them in the invisible clothing (creating a sim, planning clothes using the dresser, etc.). If you want the sim naked while they are not bathing, you need some invisible clothing. If you want to see the details when they are bathing, you need a mod to remove the censor mosaic.

These are textures only, they do not remove the censor mosaic. Any time they are naked the bits will show. package file into your Sims 4 mod folder. These were the first true skins with anatomical correctness that I am aware of made for the Sims 4.