Might this sofa be a Finn Juhl or Nanna Ditzel?  

That is Slagelse Møbelværk's logo. That forecloses the the possibilities of Juhl or Ditzel. Slagelse did a bit of work with a lot of designers.

here is a link to the sofa http://www.lauritz.com/da/auktion/slagelse-moebelvaerk-sofa-model-nr-185...

Thank you Leif and Theman, very much. Sadly I was overcharged according to what I see on Lauritz but I learned a valuable lesson!

although….
this link describes it as:
Finn Juhl (Designer), Slagelse Mobelvaerk (Manufacturer)
https://www.1stdibs.com/furniture/seating/settees/danish-mohair-settee-m...

Yep slagelse model 185.
Just got one returned after being in customer care for 15years or so.
The problem with design where there are limited resources to identify them, dealers, pros and amateur alike whants to up their lot and go by looks like, similar to and ascribed.
I have very little information for slagelse eventhough i have a vast library of books, catalogues etc.
Had a pleasant conversation turn ugly the other day as this gentleman contacted me wanting to sell the hans olsen roundette extender, BUT with only 4 and no 6 chairs.
He had no "price in mind" so i gave him the reasoning for my offer to which he blurted out " i have been offered far more than that"
Research is everything and i would love someone to publish more detail, like søborg have with their vintage catalogs.
Over to you
He was hoping that i would bestow gold upon him

Although your sofa is not in it, there is a scanned 1944 Slagelse catalog here:
http://www.kb.dk/pamphlets/dasmaa/2012/jul/smaatryk/object64679/en/

It is absolutely certain that Finn Juhl did NOT design this sofa. And there is nothing to suggest that Nanna and/or Jørgen Ditzel deigned for Slagelse, and the both of them are very well known. So it is immensely unlikely they designed it. Lauritz sold one and quoted a Slagelse catalog for the model number, and did not mention a designer. That strongly suggests it was an in-house design. To discover otherwise would probably require a lot of time and persistence and luck. Perhaps an old magazine would show the sofa, or perhaps a different Slagelse catalog might name a designer (doubtful), or maybe the family that owned Slagelse can be found and still has some information.
Sorry to hear the OP over paid for it. Is the dealer decent enough to take a return because he told you it is something that it is not?