I'm using Better Bodies, Better Clothes, and Better Beasts, and now I'm looking for some head and hair replacers to go with them. I'm also looking for mods with wearable underwear (as in actually worn under the clothes) for if and when I decide to use the nvde textures.

Any good suggestions?

I do like Better Heads, but it doesn't change the Khajiit heads.

My favorite hair mod is Westly's Corean Hair. I personally don't care for Better Heads; I use Westly's Plug-inless Head Replacer. MacKom's work looks really nice, but it seems to cause too many incompatibilities at the moment for my tastes. There are wearable underwear mods, but they're worn like clothes and won't appear under clothing. There are, however, a number of No nvde mods of varying quality.

Where can I find Westly's Corean Hair mod? Also, does this mod replace the beasts' hair too?

Hmm, it used to be at PES, but it looks like PES is dead for good now. I don't know if Westly has uploaded it anywhere else since then. I don't think it adds hair for Khajiit/Argonians, but I couldn't say for sure since I don't play as them.