I highly recommend staying at Olmo’s apartment:
The apartment is very clean and very convenient. It is right in front of metro and bus stop, as well as within walking distance to centro historico. It was a great location for exploring different neighborhoods.
In addition to the 24h security guards, the building faces a large street that is well-lit after dark. It made me feel safe as a solo female traveler. Being on a major street, there is some noise as mentioned in other reviews. I did not need ear plugs, but Olmo offers them if you need them for sleeping.
Olmo is a wonderful and generous host. He kindly gave me tips about using the metro, places to eat and see, and was generous about letting me use cooking ingredients and drinks so that I could prepare simple meals without having to buy oil, salt, etc. Although we did not overlap much of the time, I enjoyed the brief conversations I had with Olmo.