The newly-refurbished 2-bedroom apartment, on the 7th floor with elevator, was very comfortable, and located within walking distance of most of the places we wanted to visit. The small bedroom is interior (no window) with no air-conditioning of its own, but the air-conditioning in the living room and main bedroom are sufficient, if you leave the door open. There's also a foldout couch in the living room, I believe, although we didn't use it.
The owner was very sweet and helpful, and her sister lives in the building if you have a problem (which we didn't).
I'd recommend this lovely place to anyone who wants to spend a few days in Thessaloniki.