Another Chicagoan weighing in here.
Another option to staying downtown, if money reasons make it hard to do so, is staying near one of the airports. There hotels near O'Hare (the international airport) are usually less expensive. Furthermore, O'Hare is close to many kinds of public transportation, specifically the Blue Line (located in the airport), which will take you downtown
One caveat - Chicago, like NY and Boston, has very harsh winters and smothering summers, be ready to dress for it.
I hope you enjoy your stay here! I visited Chicago's sister city in Switzerland, Lucerne, and had a wonderful time.
