Here's the thing, they don't need to stay in the bedroom! Oh yes - you can show off your pretties without people asking you if you forgot to put your dress on (unless of course you know my father in law - in which case I can't help you).
The key is in layering. You want to stick with things in the same colour range, for example, pastels with pastels, jewels with jewels to keep the whole look flowing. Also, mix textures, add woolens, leathers and cottons to bring your nighties into the light - if you wore a bright red slip with black robe and black tights - you'd look like an extra from Moulin Rouge.
Here's a outfit I picked out in neutral tones for an example:
Silk 1920s beaded Robe $110 - VonlenskaVintage.etsy.com
Vintage Cappuccino Slip $34 iseefrance.etsy.com
Lacy Leg Warmers $35 smallpackagess.etsy.com
Long Brown knitted scarf $24 sapti.etsy.com
Cream Leather lace up Granny boots $59 hipvintageclothing.etsy.com
See how we mix wool, silk, nylon lace and leather for a beautiful feminine, unusual, but utterly wearable look.