I haven't cruised on Celebrity Edge and closest similar cabin was a single veranda onboard RCL Anthem of the Seas so no good advice. Cabin size can also be a little subjective depending on if you travel light, if you are used to a lot of space (NYC/Tokyo? Probably no issues in a cruise cabin), and itinerary would also be a consideration for me.

Have you checked YouTube cabin tours? I don't see a couch, just a vanity chair and two chairs on the infinite veranda. Regular infinite veranda cabins do have a small sofa. Anthem's solo balcony also doesn't have a sofa and a backless stool at vanity but does have a small cabinet near the balcony which was an extra flat surface (useful for storage). If the discount was good & itinerary < 1 week, I could McGyver a footstool from a packed shopping tote and spare pillows/towels but I'm generally ok with smaller oceanview/veranda cabins when solo as long as there's decent storage & a good bathroom. Inflatable and camp foot stools also exist.