Italian pharmacies are good, they have lots of parapharmacie products (found the LRP concealer in one, my best ever) and slightly random things like L'Erbolario and baby stuff. But expensive. I think SMN is the oldest continuously working pharmacy/ cosmetics shop in the world. Full of Japanese tourists but an amazing variety of quirky products.
I went to an unusually calm and friendly Chanel boutique in Florence and bought a bottle if 28 La Pausa (their iris perfume) - Florentine iris is one of the loveliest perfumery ingredients out there.
i second frugal a visit to smn is a must! you can shop at outlets if you like Italian designers. or just walk around,florence if full of beautiful small shops,selling everything from shoes locally made to jewelry. i have a beautiful gladiator flats,ala louboutin from a local shop there, it costed around 35 euros,very compfy.
Ooooooh I used to live there! Posh perfume shop in via della scala, totally lost on me, fab market San Lorenzo and loads of jewellery on ponte vecchio, near there opposite the boboli gardens is a lovely shop selling missoni. Avoid the cafe in the main piazza (revoir is lovely) and go to the lovely restaurant near Santa Croce .
Perfume. If you like the heady and heavy italianate style, Santa Maria Novella (lots of other products too - their toothpaste is the most stylish I've ever had) and Lorenzo Villoresi (of Teint de Neige Yerbamate fame) are locals. But basically any profumeria has a good selection, often things that are hard to find elsewhere.