I haven't been to Disney since before the pandemic, so can't speak to the situation now.
However, some suggestions in general:
I have sun sensitive skin, both naturally and due to medication. On top of that, I can't use chemical sunscreens, instead have to use mineral sunblocks, most of which I also react to - there are two brands I can use, though I will get a rash even from them given enough time.
My solution is to wear good quality Sun Protective [UPF 50+] clothing. My preferred brand is Coolibar, but there are other brands that are very good. This is not something to cheap out on -- you need to trust that their clothing actually protects the way they say it does, which means going with reputable brands that have a track record.
At WDW I wear long sleeves, long pants, a wide-brimmed hat, fingerless gloves, socks, and solid shoes. For the top I usually wear a short-sleeve shirt of my choice with an overlayer that is sun protective long sleeve [it can be a lighter weight material suitable for the weather] with a hood. I only need sunscreen on the exposed areas, which are few. I find I am actually cooler this way as the sun isn't hitting my skin [which is painful and hot] and the overlayer is light enough that it moves in the breeze creating airflow. Choosing the right weight and type of fabric is important, obviously. You still have to be cognizant of your time in the sun as the clothing is not a 100% sunblock, but I find the good stuff is more effective than sunscreen/sunblock.
(BTW for swimming, at
Castaway Cay I wear a normal swimsuit underneath Swim Protective swimwear: long swim tights, long sleeve rash guard, gloves, socks, and hood or at least hat; plus normal water shoes; works for snorkeling too. The only exposed surface is my face).
And of course you know that what people think of as "shade" really isn't so much when you have a sun sensitivity. You can still get sunburned in "shade", and "shade" from above doesn't help much with reflected sun coming up at you from the ground. Mentally, I therefore distinguish between "shade' from the sun and actual "shelter" from the sun, and seek out "shelter".
As for an
ECV, if you have done so little walking in a day I personally would give serious thought to just renting an ECV form an external vendor from the get-go. An alternative may be to contact a vendor and see what their availability would be on short notice.
But let me tell you about one trip I had a several years ago. I knew I would need an ECV so we rented one from an offsite vendor. The first night we went to DHS to see the holiday lights. We were only going to be a few hours, and I thought I would be ok, so we left the ECV in the room. By two hours in I was in a lot of pain and having trouble walking. By 3 hours was crying. By 4 hours could barely walk and as we were headed back to the room I wondered if I would make it back and how we would handle that. I was in severe pain the rest of the trip even with the ECV and it nearly ruined the trip. I should have brought the ECV that first night. And I shouldn't have pushed it once I was in pain, we should have gone back to the room.
Since then, the ECV comes if we are going to a park. It may or may not come if we resort hop, it depends on what we are planning. If we're doing a quick trip from WL to Poly for breakfast and I'm having a good morning, then we probably don't bring the ECV. But if we're planning a monorail resort hop with walking tours of each resort and a walk from Poly to GF, we probably will bring it.
FWIW, we had a great experience renting from Gold Mobility for our trip in December 2019. They arranged pickup and dropoff times that were convenient for us, the ECV was basically like new and it worked very well.
Finally, one thing I like to do to help avoid the sun, which unfortunately isn't an option right now, is going to things like the Christmas Party or other after hours-type events.... the sun is close to going down as it starts and then it is dark for most of it
Sun problem solved
OR we would start later in the day and then park hop in the evening to the park that is open latest -- one trip I remember we would pretty much park hop to Epcot each night... I don't think we ever saw Epcot in day light that trip. Unfortunately with park hours as they are right now and no park hopping, nighttime viewing isn't an option. But do consider that for future trips.
SW