Here's a little something I did for myself that I decided to share. I don't know if this has already been created (at least I couldn't find anything like it), but here you have bras that you can use as accessories.
The bras and their straps from the accessories category will display underneath tops and outfits of clothing.
It should work for all types of clothing.
The bras will come in the main colors from the base game, each with their individual swatch.
The bras will be located in the accessories category. Unfortunately, you will not be able to use the accessory bras and socks simultaneously.
Here's an in game pic.
They even show up through transparent / see through clothing.
NOTE!!! If you only want to have the bras show without clothing overlapping them, I suggest finding an invisible clothing top somewhere.
Enjoy!
Additional Credits:
Sims 4 Studio
This is a Maxis Recolour which means that it is a recolour of an item that already exists in your game. Please check the Pack requirements to see which game pack it recolours.