We would recommend you stay either in the Altstadt or Stadtmitte area of Düsseldorf. There are several small hotels which can be found on web sites such as
www.duesseldorf-tourismus.de

We shall be staying at the Carat Hotel in Düsseldorf; www.carat-hotel.de
Please mention that Elke Leinwand has reserved rooms
to get a better deal.

Another option would be Hotel Lindenhof
www.lindenhof-duesseldorf.de

For the young at heart there is also a youth hostel but this is a little further out from the city.
www.jugendherberge.de/jh/duesseldorf/