Happy to recommend places in Milan if needed - went there last year and loved it.
I'd have heavily recommended Lake Como over Sicily, personal preference! The missus & I went to Lake Como for a day trip as part of that Milan trip; stunning scenery and perfect for 1 day (not even that really, we took our time there!), and when parents have been to Sicily they got bored . Appreciate it's cost-effective though for onward journeys.
Amalfi Coast and Pompeii sounds great though. Always wanted to go there.