A raging paranoia about unattended anything in CHI is well warranted, even fire hydrants aren't safe from pilferage there.

Time for Requirements Planning.
A certain older bike would fill the bill nicely but might take patience and a few $ to get right for you.
As others have said 80's Japanese, Raleigh Technium or Schwinn mid-level bikes w/ alloy wheels that will fit fenders and a rack can be fun to ride, not attract undue attention and are not "collectable" expensive.

Get "your" frame size, no compromise here. A mixte if necessary.
Must not be beat, plenty of dusty almost never ridden stock in garages that can be yours for very reasonable $.
Ask your mechanic where your good bike came from if anything suitable is kicking about. They are tuned into a network that is wide and deep, you are in it if you ask.

Have fun. Snow starts tomorrow so prices drop and shop time opens up, and get a very good lock or two.

-Bandera