I went through my basics toward the end of December and culled five items. I also did a full count, as there were a few categories that seemed to be running a bit low and I wanted to confirm my suspicions. My totals (I don't include gear here, because that's a separate category IMO and makes up about half my wardrobe!):

Sleep shirts (long sleeve) -- 5 (all thrifted Boden bretons)
Sleep shirts (short sleeve) -- 7
PJ shorts -- 3 (one needs to be replaced)
Lounge pants -- 4 (one needs to be replaced)
At-home hoodies -- 4
Long johns (sets) -- 3 (two synthetic, 1 merino)
Bralettes -- 10, but includes one rarely-worn sports bra (eliminated two)
Knickers -- 12 (eliminated two)
Crew socks -- 8
Ankle/no-show socks -- 8
Knee socks -- 2 (eliminated one)
Camis/layering tanks -- 5
Tights -- 10 (4 opaque, 2 sheer black, 2 fair isle, 2 ribbed)

I got rid of my two oldest bralettes due to shot elastic, and also culled two pairs of cotton briefs that never fit right. I said good-bye to an ancient pair of wool knee socks that finally developed holes in the heels and toes after more than a decade (!!).

Going into 2019, I'd really like to add:
1 - 3 pairs of PJ shorts (I wear these every night and will soon be down to two pairs if I don't add anything new.)
1 pair lounge pants (to replace an old threadbare pair)
2 - 4 pairs knickers (to maintain my laundry schedule I really need at least 14 pairs, so I'm a bit short right now.

Other than that handful of categories, my numbers feel reasonable for my lifestyle. (Okay, 10 pairs of tights might be bordering on excess, but they do all get worn a couple times a year!)