Düsseldorf has plenty of hotels to choose from and at a varied price-range. I am listing here a few hotels that I can recommend and that are within walking distance of the conference venue. As there is a dense net of public transport surrounding the city centre, you are of course always free to choose a location that is further away.
Right in the heart of the Oldtown (incl. party and noise)
St. Georg (http://www.altstadthotel-stgeorg.de/index.html)
Barcelona Bed & Breakfast (https://www.altstadthotelbarcelona.de/de/)
A walk along the famous Königsallee away
Wyndham Gardens (https://www.wyndhamgardenduesseldorf.com/de)
Two Tram-Stops away and still walkable
Hotel Windsor (https://www.windsorhotel.de/hotel-windsor/)
Chic and Boutique
Hotelfriends Düsseldorf (https://www.hotelfriends.de/)
Dusseldorf Hostel (https://www.jugendherberge.de/en/youth-hostels/duesseldorf-442/prices/)
YOU MAY WANT TO HURRY A LITTLE BOOKING THESE, AS THE CHRISTMAS MARKET OPENS EARLY THIS YEAR (November 23rd) AND ATTRACTS A LOT OF TOURISTS!