Another issue is that hotels in general don't have a "room standard". I lived quite some times at Scandinavia Hotel in Copenhagen this autumn, and I always got a double room when I had booked a single. (Looking at the floor plan on the door it was evident that my room was of the bigger category of rooms on that floor.)

The week after I arrived late and got upgraded to a business class room. Difference: none... except for the bathrobe. I got the exact same room, 10 floors up...

At the Scandinavia Hotel in Oslo they were quite nice. The guy made a point of looking for a nice room for me, and apologized for not having a Business Class room available. I got a recently refurbished superior room with a view. Quite nice. The superior room was tiny though, hardly any space to walk around the bed.

(Oh, and why do they always upgrade me into useless twin-bed double rooms? I can only sleep in one bed...)

Another thing is that the policy states that we can get an upgrade in the same room category. Tommy; you might want to ask for clarification if a single room and a business class room is in the same category.