We travelled a bit in the area and I must say that Ruben E Stefania's place has been where we have felt the more 'at home'. The premises are modern, clean, the breakfast really good with biscuits and fruit available all day long.
The place is just next to the National Museum, 10min by foot from the historical center and ~20min by foot from the Piazza del Plebiscito.
It was really perfect, thanks