I've been using Samsungs One Hand Operation+ for a year. It can be installed as a standard app from the galaxy store. It uses 7 mb of storage, 28 mb of memory, 0 mobile data, and 0 battery after set up.
It adds a thin handle to the left and right side of the screen. We can change the color, transparency, position, length and swiping distance. I set the one on the right to take a screenshot. The one on the left turns the display off. Swipe options are Straight, Diagonal up, Diagonal down and each one can preform a different action.