Unless you are severely allergic to cats, I definitely recommend Kevin and Sarah's Air Bnb! The room is spacious and comfortable, plus the view from the window is very nice (especially at sunset). Sarah and Kevin were very kind and helpful during my stay. I went to a few restaurants and cafes that they recommended and they were all great! (The cafe next door was fantastic.)Their cat is extremely cute:D
You do have to climb up the hill a little bit if you are coming from Edinburgh Waverly station. But there is a step-free, relatively easy route to the flat. If you are carring a heavy suitcase, search the Google map for bicycle routes.