It's long and it's hot, but it isn't that bad of a walk at all. I already do miles upon miles per day at Disney Parks; what's an extra 1/4 mile or so? And by the time you're done taking several buses to transfer to an Epcot Area resort to take the boat (unless you're staying at one), what have you gained other than a minute reduction in steps? Is it worth taking a bus from your resort to DS to the Epcot Resort to HS? Not to mention all the walking you'd have to do from the DS drop off to the Epcot Resort Bus Stop.
I measured in Google Earth using Path Measure and it's actually a very slightly longer walk from where buses drop off at Epcot to Bag Check.
From the bus stop for OKW to Bag Check at HS was 0.21 or 0.23 miles. From where the bus drops off at Epcot to Bag Check was 0.24 miles. The usual Pop bus stop is about 0.24 miles as well.
It's 0.25 miles from the bus drop off to the farthest stop in the Bus Loop for DS, and 0.21 miles from drop-off point to the farthest stop in the middle of the bus loops at DS.
The path from The Little Mermaid Room Building to the Bus Stops at AoA is 0.34 miles.
If walking and being in the sun and heat are things you're trying to avoid (and that's the Royal You, not singling any one person out here), then a Disney Parks vacation in Florida (or SoCal, for that matter) is probably not a great idea.
If it's a medical issue, there are courtesy wheelchairs available and it's entirely probable that Disney CMs would work to accommodate your needs. (Especially in an emergency situation.)