Searching for a charming place with 2 beds, kitchen in Dusseldorf.
When in Düsseldorf I stayed in Hotel Bismarck, a 3 star place, ca. a minute or so across from the Düsseldorf central station. It's a nice charming place, very old school, projects a genteel image, good breakfast buffet, not lavish, have stayed here several times. I don't know about the kitchen factor.
I don't prefer staying in Düsseldorf anymore, nothing wrong at all about Hotel Bismarck.
Now I rather stay in Dortmund right in the train station area, cheaper and a bit more luxury relative to the price compared to Hotel Bismarck, plus better train connections, day and night.
If you want something with a kitchen, try looking on Booking.com, you can sort by that amenity, or what you might need (refrigerator, microwave, etc) as well as number of beds.
In Dusseldorf the old town is a bit away from the main train station, so you have several areas you could pick, depending if you want to be in the old town, near the river, near the station for trains, or in other neighborhoods. Each has it's advantages.