GET GRIPPER BARS! Get ADA approved gripper bars for shower sex. The person on the receiving end can lean forward and grab the bars, making shower sex safer and more fun.
These bars start at less than $25: Moen 8942 Home Care 42-Inch Grab Bar Stainless 42 inches (4.8 out of 5 stars from 158 reviews on Amazon, but none mention sex). Also: Moen 8736 Home Care 36-Inch Grab Bar, Stainless , 18″ to 42,” (4.8 out of 5 stars from 322 reviews, but none mention sex).
The Moen Saftey Bars are rated at 500 lbs. pull strength and are ADA compliant—not that the ADA rates equipment for shower sex.
Also, if you are using a silicone-based lube, be sure to put it on while you are standing over a towel. One drop of silicone-based lube on a wet shower floor and you might as well be on slick ice.