Camisoles create versatility in a wardrobe, instantly changing any outfit they are added to. To build a wardrobe of camis, I would suggest first figuring out what neckline flatters you the most, and would work with jackets/tops you like to wear. Camis can be straight across, v-neck, scoop neck, ruched, and come in a variety of materials and price ranges. If you’re planning on using a cami primarily for layering, thin (but not see-through) is preferrable; the fit of it on your body should be form-fitting, but it doesn’t necessarily need to flatter if it’s going under other garments. Also, it is often better to buy a longer cami so that the bottom can peak out under tops: if the cami is shorter than the garment over it, you risk giving your waistline an awkward, severed look. Bra shelf camis are not necessary unless you like extra support; for bustier women I recommend still wearing a bra or sports-bra under such camis. 

Closet suggestions:

Basic black cami

Basic white cami

Cami with lace top (any color)

One cami of a nicer material, like silk. 

Basic camis can be found at just about any mall clothing store. For a silky cami, you can even try the lingerie or pajama section of a store.