Francesco's apartment is very cute, bright and colorful. Clean. Perfect for two people. Paula greeted us on arrival and the key exchange was easy. I would recommend taking an ub*r or taxi from the airport if you have bags because it's about a 10 minute walk uphill from the train station (doable but not fun with suitcases if it's hot).
Location is great, close to restaurants, the famed Alfama flea market Feira da Ladra (Tuesdays & Saturdays) is a block away, the Panteão Nacional, the 28 tram line, the Santa Apolónia train station.
There is no air conditioning, but even when it is 30 c during the day it doesn't get unbearably hot at night with the window open. I imagine mid summer might get quite warm though. Shower is a bit small but the water pressure was great.
Not recommended for people with mobility issues as the apartment is upstairs and the bedroom is upstairs inside the apartment.
The outside door into the apartment building is hard to shut, you must gently close it and then lift on the lock to get it to shut.

Our only issue was not related to the apartment, but the attached building which is under construction and as such we were subjected to drills and saws and hammering from about 8 am most mornings. I'd recommend bringing earplugs until the construction is done.
Check out "...do Vigário" cafe (rua do Vigario 74) for the best mazagran (a type of iced coffee, it's a bit tangy and delicious, closed Wednesdays)