I tried shade sails several years ago for the same reason - to try and keep water temps below 90°. Didn’t work for me. I had overlapping sails going from end to end of my pool and almost the full width. What I discovered was that due to the angle of the sun, the pool was rarely fully shaded and almost always less than 50%. Unless you get the sails very close to the surface of your pool, you may have the same issue.
Do you have a way to secure shade sails temporarily? Before investing in a permanent installation, I’d try testing first. Of course, if you are also wanting the shade sails for shading the decking or for aesthetic reasons, that’s a little different, but you may still want to test them out first. You can get relatively inexpensive sails online. I used parachute cord and turnbuckles to secure mine to trees that surround my pool. The challenge was constantly taking them down if it got too windy for fear of snapping a tree.
I ended up with a Glacier chiller, which works beautifully. My pool water is in the upper 70s in the morning and doesn’t get above 83° even with ambient temps over 100°. I would expect that it would work even better in your less humid environment. Probably about the same cost as a professionally installed sail shade solution. And I don’t have to worry about high winds, which would be a concern regardless of how they’re anchored. Just a thought.
Good luck with whatever you do! I can relate to having a pool and not wanting to get in it during the hottest part of the summer, which is kinda ironic.