The free ticket covers entry to the basilica; the price list says people with disabilities pay only for added services, and a companion is free on the basic basilica ticket (4 euros if a guided tour is added). You still need to reserve the timed ticket online in advance, as every visitor does, and to bring official proof of the disability, which staff may ask to see at the door along with photo ID.
The towers are the one part to leave out. The conditions of sale exclude wheelchair users, people with reduced mobility, and anyone with vertigo, claustrophobia or heart or breathing problems, because the way down is on foot. Nothing is lost for prayer: everything else, the nave and the Chapel of the Blessed Sacrament included, falls under the basilica's statement that all of it is accessible.
Good to know before you go: the basilica lends wheelchairs at entrance B but does not guarantee one, so bring your own if you depend on it, or ask ahead through the visitor service, whose phone and email are on the basilica's FAQ page. Guide dogs are admitted with the people who need them. Visitors with pacemakers or implants, and pregnant visitors, can pass the metal detectors safely but are asked to tell the security staff first. The basilica's pages read on October 10, 2026 do not describe its restrooms or lifts, so ask the visitor service about those if they matter to your visit.