I wouldn't worry about the sheep getting too hot - cold is more of an issue.
If they have a lot of fleece on, it also protects them from the heat. Just make sure they have access to water and shade and they'll be fine.
We have very wooly sheep out in the summer sun here and it's not a problem for them.
Did you check out the videos of kiwis shearing sheep? You can see how they stand and hold the sheep so it doesn't struggle, and how they stroke the fleece off.
it's pretty impressive stuff when you watch the really good guys do it - shearing a sheep in just a few seconds.
I haven't done the actual shearing myself, but I have been a sheep dog on occasion ;-)