We're visiting Florence, Rome, Salerno, Taormina for 16 days in early April 2025, traveling by train north to south. Rule of thumb in past years was to book everything 3-5 months in advance to get the best air rates, but we've seen the trend, add Jubilee 2025 on top & so we said screw it and booked everything over the last few weeks. Air, apartments--done. Booked The Tour Guy for Vatican/Sistine/St. Peter's, where in past years I'd do it on my own. And when train reservations open up 4 months in advance, I'll book those as well.
Last two trips to Italy have been in late February/early March, and it's been chill & delightful. Those days, unfortunately, are gone. It'll still be great, and at least it won't be in July/August with the heat. Crowds and hot temperatures in Florence & Rome sound like a disaster to me.