What if they attack me for Southern Italy? Then what?
Are you not allied with anyone? Muscovy? Bohemia? And if they charge your way do you have forts on mountain tiles?
Allied them already, and I am in the process of overhauling my army. I integrated a lot of land so the soldiers I picked up aren't always what I wanted. I'm working towards quantity ideas and I am already allied to those you mentioned.
Why quantity ideas? France already gets a ton from it's provinces and its national idea so it's somewhat redundant. Quality is a much better option, especially in this case.
And you can still defend your italian provinces. Either force them to meet you in the Alps where they'll get -2 or -3 modifier when attacking, -1 or -2 modifier if they're marching on Paris or stackwipe them 1 by 1 if they're crossing the adriatic straight to south italy.
Obviously you can't match on the attack so stay defensive. Either you'll win on the defensive and deny them their wargoal where you can empty the Ottoman bank or you can always wait it out and fight an attritional war until their war enthusiasm reaches 0 where you can simply white peace it out