If you are traveling with two people, stop looking and book Katerina's apartment now.
My wife and I have stayed at over 100 AirBnBs in the USA and Europe, and our experience here was one of the very best. This place is just perfect: from the location (literally 3-4 minutes walk from the train station, and within 30 minutes of all the main sights), to the cozy and comfortable space + full kitchen, to the wine, beer, fruit, and snacks waiting for us when we arrived, to the shower toiletries, to Katerina's excellent and prompt communication and her generosity in allowing us to delay our check-out -- everything about our experience made us feel at home here. The bed is very comfortable, the bathroom is amazing. I could go on. We're truly grateful to have stayed here and will certainly be back next time we're in Prague!