I was a solo female traveler in February (2016) and I loved D'Osma. Safe, clean, great neighborhood in Barranco, and easy access to the Metropolitano (the public bus system with a dedicated traffic lane, kind of like a light rail system). The staff were wonderful!
However, D'Osma allows smoking in their courtyard/patio area. I would have seriously reconsidered staying here if I knew that. My room (which was very nice) was located on one side of the small courtyard, with the office/kitchen/entrance/exit on the other side of the courtyard. If I were to enter, exit, go to the office, go to the kitchen, and/or return to my room, I had to walk through a cloud of smoke. There was a guest who was constantly in the courtyard smoking. The kitchen has window "slats" facing the courtyard, which you can't close, so even the wonderful breakfast each morning was spoiled by cigarette smoke. Please adjust your policy about smoking or inform guests of this in advance!