How do you decorate your place frugally?
Decorate with things you love.
For example, some people have bicycles they love riding and display them as art. Especially if enjoy using them and it makes it easier to use.
Another thing might be a camera or an instrument. Even a video game controller. Craft supplies. A favorite blanket.
Put those things on display.
Another aesthetic? Super spartan. Put everything away. That is the equivalent of dressing all in black.
Either would work.