I second Savoy as a good option for Minor > Italy > Roman Empire.
Savoy has good traditions of + BROT and + diplomatic relation, both are very useful for a Italy / HRE start. Savoy also has a number of different expansion options in the early game, makig it less dependent on rng. Focus on attacking anyone excommunicated by the Pope (frequently: Florence, Milan, or Provance) and move into Iberia once your ally France is willing to support you in war.
I might post some screenshots of my current Savoy game once I get home tonight. I didn't break any speed records in forming Italy, but it's late seventeenth century and I'm very much on track for forming the Roman Empire.