I purchased an umbrella like you are describing on
Amazon to use specifically at WDW. Here's what I found:
First of all, you *will* at some point find that the sun is coming underneath the umbrella and there will not be enough adjustment to keep that from happening. Just frustrating - and because you tend to be moving through crowds, etc. you have to make sure that your field of vision isn't impacted by the angle of the umbrella.
Next, it is a giant pain in the butt every time you want to get on/off of the
scooter. If you put it high enough that you can kind of duck underneath, then you will either poke out someone's eye who is walking next to you, or you will block the vision of everyone behind you - and they won't be happy about it either. You don't realize how often you get on/off of a mobility device at WDW until you have something like an umbrella that you have to deal with constantly.
Finally, most of the umbrellas that you will be looking at for this purpose will tend to swivel with the wind. You don't think of Disney as a windy place... until you try to drive an
ECV with an umbrella attached! Suddenly, the wind is swinging it around in directions you don't want, and every time - no fooling - every time - I turned a corner, that damn thing swung around on me until I got mad, and it wound up in a Disney trash can. I was about $30 poorer, but a whole bunch happier the next day when I went and bought a big old floppy brimmed hat to wear for the rest of the trip.
Don't do it...
Also, I know you are real excited about the idea of folding that scooter and walking on the bus... but do yourself a favor, and just ride it up the ramp.
My personal Travelscoot weighs only 35 pounds without me, and folds down to a size where it will fit into a golf bag, and I *never* fold it at WDW. Drive it on the bus - it will be too clumsy and cumbersome, and even if you can lift a 50 pound box no problem... a folded mobility scooter at 44 pounds will not be easy to drag up and down the steps of a bus.
But what do *I* know? I've only been doing this for years now...