This flat is great if you want to party hard. It is located right at the epicenter of Barrio Alto where people party in the streets until very late hours, however if you want to rest at night, the flat is very noisy (the host even offered us earplugs). Regarding the host, she kindly received us at the flat, gave us some very usefyl tips and even allowed for a late check out. However, we had problems with the mattress and, unfortunately, she could not help us resolving it. I guess she does not live there, but rather it is just a place she rents out, therefore the quality of the mattress is not regarded as it is was her own.
In summary, very noisy flat with extremely soft mattress (we were literally feeling the mattress springs in our backs) resulted in little rest and severe back pains. I would certainly return to Lisbon but would not return to this flat again.