The currents of thought were three:
1) Someone pointed to the language of the courts of central-northern Italy (an example comes from the books of Baldassarre Castiglione, or from the Orlando Innamorato of Boiardo);
2) Others (like Machiavelli) pointed to the modern Florentine (sixteenth century);
3) In the end the position of the Venetian Pietro Bembo prevailed, who proposed to refer to the Florentine literary model (fourteenth century), especially Boccaccio for prose and Petrarch for poetry.
Consequently, the written Italian was modeled on this fourteenth-century Florentine “golden”, while the sixteenth-century Florentine “silvery” continued its evolution. Even the modernizations proposed by Manzoni (who for the Betrothed wanted to adopt the language used by the cultivated Tuscan classes) did not change the structure of the Italian language much.
In fact in Italian “standard” many of the evolutions present in the modern Florentine are missing:
the gorgia (that is the spirantization of the p, t, c intervocalic),
the reduction of the diphthong uò (in Italian it is called man, new, in Florentine instead òmo, òvo),
the “dragging” of c, g pastries (in Florentine it is called bascio, crosce, sgènte).
Consequently, it can be said that the Italian preserved the pronunciation of the ancient Florentine and expelled some localisms: it is a sort of Florentine “purged” with more local characteristics. Nowadays, especially in the city of Florence, the two linguistic registers are very closely intertwined: the standard Italian is very much influenced by the Florentine, and the dialect has gradually become Italian.