I think
Crocs are just about ideal for that type of weather. However, I can't wear them all day. If it's not raining, I bring sneakers and high quality sandals. The type of sandals I've worn has varied over the years. One brand I really like is Ecco. The style I prefer is a little like a BIrkenstock, but black, with three straps across the toes and one strap around the ankle. Other companies that have made similar style sandals include Teva (not quite as comfy a footbed for me) and Clarks.(not quite wide enough for me). Other DISers swear by other high quality sandals. I like black because it kind of matches all, and also looks slightly less bad at dinner (no sandals are ever going to be high fashion)
One thing I like about hte kind of shoe I describe above is that you can adjust all of the straps as needed. If your foot swells, you can make them loose, if the straps start to stretch out - you can tighten the straps to prevent rubbing.
Another thing I think is important at WDW is to alternate shoes daily as much as you can.
One more thing that really helps is moleskin. Find it at any drugstore where they sell foot stuff. You have to cut it up ahead of time, but it works to proect tender spots. I'm ont prone to blisters, but I once ha d abad cut on my ankle just before WDW. Moleskin saved the day.
One other thing I try to do - soak my feet/legs at night in warm water. Often enough we'll go down to the resort hot tub. other times I just fill the bathtub in our room. Ten, fifteen minutes really makes a difference. Soaking your whole body feels great, but the critical thing I find is to soak my legs up to my knees. It isn't as effective if you wait until the morning. If I'm at all sore, I soak, no matter how tired I feel.
Oh, and one more thing....toughen up your feet before you go - if you can. Walk barefoot outside! Do this in the summer especially, on a hot sidewalk. Always before WDW I like to 'get in shape' walking 30min or more each day for a month before I go. I can't say for sure that prevents blisters, but it really helps keep me from hurting.