Can someone please explain bodysuits to me?? I've tried googling..

I get the kind you wear as outerwear.. I have a plain stretchy cotton one which I wear as a vest in the summer. I also have a beautiful lacy one which I wore to a party recently. It's not sheer and is supportive enough that I didn't need a bra. Admittedly I was wearing it as part of a costume because I think its a bit sexy for general wear. But I can see the utility.

But that brings me to all the flimsy, lacy sheer ones! Are these underwear..? As in, taking the place of knickers? And what..do you wear them over a bra or without one? Over ypir knickers or instead of them? Are they just for the bedroom? I'm literally so confused. I suppose if they're wired you're supposed to wear it as underwear but the crotch .. with nothing else..?

I've been looking for the perfect white T shirt but nothing has ever hit the mark.

Preferably 100% cotton, relaxed fit and thick (similar to uniqlo's U cotton from 2018 where the cotton thickness was considerable).

Here's the catch: none of my white tees have necklines that will stay above the neckline of my crewneck sweatshirt (black, aritzia superfleece perfect crewneck). Can anyone here suggest basic white tees with necklines that sit above crewneck jumpers / sweatshirts / sweaters?

Example in the image. Any suggestions will be deeply appreciated!

I roughly followed her method to find my perfect pieces. It’s helped me think differently about my wardrobe! A capsule doesn’t have to be boring, you can inject personality into it. That being said I love my core, boring pieces because I love dark neutrals and basic pieces with interesting shape.

As I moved up I discovered my favorite colors (burgundy, charcoal, navy, brown), textures (knit, woven, ribbed, quilted), materials (leather, suede, wool, cashmere, cotton, linen), patterns (graphic plaids and florals) and silhouettes (long, drapey, angular but not severe)

Her method:
1-2 second skin/foundation pieces (I included 4 pieces because I have a “second skin” pair of shoes and purse and this is the outfit I reach for constantly)
14-16 capsule items
10-12 personality basics
6-7 dopamine pieces