Walking or vaporetto

When I stayed in and Air bnb in that area last year, the owner gave us very clear directions to a vaporetto stop, and also arranged for a friend to meet us at the vaporetto stop. (I also used google maps to see exactly where the Air BnB was, just in case we missed the connection at the vaporetto stop.) We communicated via WhatsApp, which is how I let him know when we were getting on the vaporetto near the train station. Have you been in contact with your Air BnB folks to get directions from them?

It is pretty central to San Polo, so I don't think a vaporetto will help. Walk it with google street view and you'll see 2 bridges with about 10 steps up and down, and one bridge where a ramp has been added. Streets look to be paved with flat stones, none of those annoying cobblestones.

So if your suitcases have rollers, no need to cough up 100 EUR for a water taxi. Its only about 1/4 mile.

Or, you can take a vaporetto (#1 or #2) to San Toma. Then you can walk to your AirB&B without any bridges (Google can show you the way).

It's about a 5 minute walk from the San Toma vaporetto stop. Getting there on the vaporetto would take at least 1/2 hour, probably more because it's a long ride. On the other hand there's a lot less chance of getting lost than if you just walk from the bus stop. I'm not very good with google maps but it looks like there are no bridges from San Toma to Calle de San Nicoleto.

The vaporetto #2 will have a less stops to San Toma.

and if you take a vaporetto you get a tour of the Grand Canal to boot.

And if you buy an x-hours (24/48/72, etc.) vaporetto pass for the duration of your visit the marginal cost in and out is zero.

Don't get vaporettos (effectively water buses which ply a particular route making scheduled stops) and water taxis (which are what they say they are, taxis on water providing private transportation from A to B for lots of money) mixed up. They work very differently and cost dramatically different amounts of money.

I'd take a vaporetto. We've stayed in the San Polo area a few times - luckily our B&B is a one min walk from the San Toma stop. But once we decided to walk from the train station as we were arriving very early after an overnight train ride. We had the benefit of knowing where the B&B was since we'd stayed there before, but I recall some walking over bridges and whatnot. Time of day may make a difference - if you're arriving during a busy time of day, you'll prob have lots of tourists to contend with, along with your luggage. Are you arriving after an overnight flight? If I was tired and jetlagged, I'd rather just take the vap.

Expect to get lost.

I think that the vaporetto from P. Roma to San Toma is easiest, and either the No1 or No2 vaporetto is OK, both stop at San Toma.
From Campo San Toma vap stop, there is only one calle to walk up. Turn right at the tee, and then from Campo San Toma, head towards the octagonal pepper pot of the Frari campanile. Head left into Campo San Rocco, past the church of San Rocco, and your calle is on your right.
Five to ten minutes walk, nd no bridges.