Traveling with someone that cannot climb stairs

Unfortunately, four of the five Cinque Terre villages have lots of stairs; they are really up and down. The one that has the least stairs and is the flattest is Monterosso al Mare.

Would you consider to take the boat to experience the towns from the seaside? Some of the most beautiful views, actually.

I would absolutely avoid the Cinque Terre, and the Amalfi Coast as well. It is hard enough getting around in cities like Rome with physical limitations, in small towns with many stairs I can just imagine the suffering.
A boat ride would be a nice alternative, although if you ask me not worth it as far as travel and expense is concerned if you cannot get in and enjoy the towns themselves. The views are especially wonderful from the land out to the sea.

I guess going completely out of your way to get to the Cinque Terre only to do nothing more than a boat ride is probably not the best use of your time. But if you're in the area (e.g. want to see Pisa anyway), than this can be a nice day trip:

Go to La Spezia in the morning and get onto the boat.

Take the boal all along the 5 towns to Monterosso, takes about 2 hours.

Embark in Monterosso and walk around a bit, it's all pretty flat close to the harbour. Maybe have lunch.

Take the train to Manarola. Walk the Via Dell' Amore to Riomaggiore. This part of the trail is wheelchair accessible and all flat. Takes about 20-30 minutes if you don't stop. Half way on that path is a little cafe, you can sit down have a coffee or lemonade.

Explore a bit of Riomaggiore and take the train back from there to La Spezia.

I don't know if it's possible to visit anywhere in Italy without climbing stairs! Seriously. We have a disabled son I would love to vacation with eventually, but on our trip to Italy - north to south - I could not picture bringing him or his wheelchair.