I like to use a piece of the real thin wood, I think it's called masonite for printing pockets.
For fixing prints I have a frame I made a few years ago with no mesh that I tied several parallel strings across. I mount the frame in an open arm of the press. Then I do a test print of the fix, lower the string frame, and tape a piece of cardboard onto the strings so that the top edge is exactly where I want to position the existing print on the shirt. Now when I load each shirt I can lower the string frame and use it as a guide to maneuver the shirt into the exact position.