I can highly recommend Monika's apartment. The location is within walking distance (15 min.) from the archeological site of Ostia Antica. Grocery stores/bars/restaurants/cafés are nearby. The apartment itself was well-equipped -- from drinking water to coffee and a small breakfast. Monika even helped me in an emergency: I was trying to reach the airport by bus, but the bus never arrived, so I tried to get a cab, but the bar owner calling the cab service said they were all booked, I then called Monika who happened to be available and immediately offered me a ride to the airport for €20. Thank you again, Monika! :)