We had a joyful stay at Joyful Guesthouse and Ilaria helped us with the itinerary. The place is in the centre of the city so we only took the metro to go to Vatican but we walked our way back as Ilaria has pointed out a few attractions on the apartment's direction.
The room and the bathroom are very clean and you are offered cereals/yoghurts/croissants for breakfast. Actually, it looks exactly like in the pictures and as described by the owner.
We are using airbnb for some years and this is one of the nicest places we've stayed in.
We will definetely stay here when in Rome next time :)