Limelight, Pinky Winky and Quick Fire hydrangeas can take the heat although they'd also do fine with some shade. I'd try these varieties first before draping a shade cloth over them, so you didn't have the hassle of remembering to do that every sunny day. But if that isn't an option, Gardeners Supply Company makes some covers that might work for you.

Hi Emily, I so appreciate your taking the time to send some ideas my way. I'm afraid I am an oldfashioned Hydrangea fan, loving the big mopheads I grew up with and that is what I have on my deck. Gardeners Supply was one of my first places to look and I just can't believe that someone hasn't created something along the lines of a small umbrella made of shade material. I am currently using a Little Tikes umbrella because it is short but it just too big for what I need. Thanks and again. Connie

Get a patio umbrella and remove the fabric and use shade cloth on it. That's a great idea!

Umbrellas have been used for shading peonies for a long time. Like this:

https://www.treepeony.com/products/garden-umbrella