If you are traveling to Sardinia and you don't want to take the plane there is the ferry alternative.
The Moby ferry was big. There is a playing ground for children, a canteen, a restaurant, a bar, a small shop.
The external room was small, but decent given the circumstances.
We paid about 260 euros for a return ticket for 2 persons in an external room and one car in off-season (in November). The food on board is rather expensive at the canteen - 2 main courses, 2 desserts and 1 drink - about 20 euros.
The trip from Livorno to Olbia takes all night (leaves around 9 PM and arrives the next morning at 7 AM).