Per the expert, Rick Steves:
A €15 combo-ticket covers Duomo-related sights: the Baptistery, dome, Campanile, Duomo Museum, and Santa Reparata (the church crypt, inside the Duomo). You should only get the combo-ticket if you don't have a Firenze Card (which covers the same sights).
Blockquote
Where do I purchase such ticket?
I went to the website included in the above article, however it only offers the Firenze Ticket which does not suit our time in Florence. I know that I can purchase the Academia ticket separate, but interested in the Duomo -related sights as well.
Thankyou