Use
google flights,
kayak,
momondo, or
skyscanner. Think you can get flights from Manchester for about £85 return with a stop in each in direction going the day before coming back the day after.
From London it looks like you can go direct for about £25-30 return.
Depends when you want to fly, where you want to fly from, and where you want to fly to.
Its a straightforward journey and is fine to get there - Italian trains, especially the Frecciarossa's are excellent. Last train back seems to be at 21.10, and the game kicks off at 21.00 local time so think you might need to stay in Milan for at least the night of the game!