The 29-year-old scored just once in 15 league appearances for Milan before making the switch to Florence for the rest of the season during the January transfer window.
Matri scored twice on his debut - a 3-0 win at Catania last month - and says he is enjoying his football again after finding "peace of mind" in a new environment.
"I was in a tunnel at Milan," he told Gazzetto dello Sport.
"I wanted to do more there, but I failed. I take all the responsibility for that.
"But I was doing it internally when I was there. [Vincenzo] Montella has given me the one thing that I needed - peace of mind.
"I suffered with a lack of confidence, but I came here and scored straight away which made me feel a lot better."
Fiorentina currently sit fourth in Serie A, just three points off the third and final Champions League spot, and they reached a first Coppa italia final since 2001 courtesy of Tuesday's 2-0 win over Udinese, sealing a 3-2 aggregate triumph.
La Viola take on Inter at the Artemio Franchi on Saturday.