If I'm not to late to offer up a hotel, you can try this one, it is more of a B & B then hotel, only has 10 rooms, owners live on site, 25 minute walk (for me) to the Dom, and reasonably priced.

Hotel Im Kupferkessel on Probsteigasse

Here is their web page, www.im-kupferkessel.de/
if this is not the English link, just click on the UK flag.
I always try and stay here when I go to photokine.

Another is this one. http://www.coellnerhof.de/service_e.htm
I've stayed here 5 or 6 times, there was never a problem at any time.

Wow I sound like a commercial for these hotels. Think I should ask for a free Kolsch, the next time I visit.??