I am nearly 80 and have just spent a week in Venice. We stayed in Airbnb very near to the Giardini Waterbus stop. We bought an 7 day pass for the waterbus so were able to travel all over the area without further cost. We bought the pass the minute we arrived at the Station and went to all the well known sites including the Murano & Burano Islands. If you can’t walk too far this method of transport is ideal and very much cheaper than the water taxi. I went with my daughter and one of my grandaughters and we all agreed that the waterbuses were a terrific way to travel. Our hostess provided us with free wifi which was great. We travelled by train, Eurostar to Gare Du Nord, then metro to Gare du Lyon and finally Sleeper train to Venezia S. Lucia. The sleeper train was okay but rather cramped particularly with the ladder out. It was not much fun sleeping in our clothes ( had to do this as unknown gentleman was sharing with us) and the customs men in Switzerland woke us up just when we finally got to sleep (about 2am) The bunks were three tier but I let my daughter and grandaughter take the top bunks! it was a new experience for us but I don’t think i would do it again. We were lucky to be near the public parks as most of venice is heavily built up.
