You certainly do not need to sit inside a villa all day
Get up early and maximise the 8am -12pm time slot.
Or go out later and enjoy the after 6pm till later time a slot. The new FPP is your friend here.
Hydrate, hydrate, hydrate.
Eat lunch in air conditioning.
Hydrate, hydrate, hydrate.
Eat dinner in air conditioning.
Know where the longer air conditioned rides/attractions are in each park and use them when you need them. Many have short queues. Hall of Presidents. Ellen's Energy Adventure. Nemo. Lion King. Tiki Birds. Carousel of Progress. American Idol. Country Bear Jambouree. The Living Seas. Walt, One Man's Dream. Turtle Talk with Crush.
If you're not visiting the loo, you're not drinking enough. Hydrate, hydrate, hydrate.
Listen to your body. If it's thirsty give it a drink. If it's too hot get it inside an air conditioned shop or fast food place or attraction. If it's tired let it have a rest.
Enjoy the pool.
Wear comfy, worn in, supportive foot wear. Blisters can be the thing that makes the heat just too much to bear.......
We almost always go in August. You'll be fine.
Enjoy
Ps. Hydrate......