Sounds like you've got it in the bag. What you ought to do now is instigate a civil war in Italy, bring back a few of the dead factions and start all over again with the Horde on your back!

A similar suggestion would be to try Caravel mod. You will not regret it.

I was having a wonderful time playing the English, I had subdued France and was intending to make a fine, technologically advanced nation on the continent from which to strike out against the Holy Roman Empire, when all of a sudden the Scots invade.
The Scots are not a faction in Caravel, which retains all vanilla features. So yes, I was invaded by the Scottish Rebels and lost all of Britain because wouldn't you know it, my two provinces producing Hobilars - the only units I had which could counter valour 2 Highlanders - were Northumbria and Mercia.
Somehow the Scottish rebels had increased from about a stack to two stacks of Highlanders in forty years, and although I had two armies, these were both in southern France and consisted of Urban Militia with two battered units of Hobilars.

I was meaning to tell Gollum this, as I am sure he will find it amusing as I found it amusing and frustrating, but I certainly recommend you have a go at that if you are finding this Italian campaign too easy.

Or perhaps you like battering Europe so easily!

Anyway, please update us again when you can and post some pictures of all this!