Livraria Lello is worth seeing for the building. It is not where I go when I want half an hour of quiet book browsing. For that, Porto has better, less crowded stops, each with a different kind of shelf.
If the staircase is the point: Livraria Lello
Livraria Lello at Rua das Carmelitas 144 is a beautiful, busy attraction. It uses timed, ticketed entry; buy through the official ticket site before you go. I would go for the carved staircase, stained glass and the room itself, not expect a hushed reading hour.
For Portuguese books and a local literary room: UNICEPE
UNICEPE is upstairs at Praça Carlos Alberto 128-A. It is a cooperative bookshop with a strong Portuguese poetry and fiction selection, and it regularly hosts book events. You may walk past the entrance if you expect a large street-level shop; look for the upstairs address. Its site lists the schedule and events.
For a general independent bookshop: Flâneur
Livraria Flâneur is at Rua de Fernandes Costa 88, near Casa da Música. It is a general bookshop and publisher, with a calm neighbourhood feel; I would go here if I had time to browse widely rather than queue for a famous interior. It opens Tuesday–Saturday, 11:00–19:00, according to its own page. This is a separate trip from the old centre, so pair it with Boavista rather than squeezing it between Lello and Ribeira.
For a convenient browse: Bertrand
Livraria Bertrand at Rua da Fábrica 90 is an easy central option if you want a broad selection and do not have a specific independent shop in mind. Check the branch’s current listing before going.
If you want a book connected to Porto, ask for Portuguese writing in translation, local history, architecture or photography. UNICEPE is the one I would choose for Portuguese-language discovery; Flâneur for a broader independent browse; Lello for the architecture. Those are three different visits, and none needs to pretend to be the other.
