Cotton compresses down to nothing when wet. Then there is no cushioning. Acrylic yarns like in Thorlo socks don't compress down nearly as much, providing better cushioning throughout play. But even with Thorlo's you've got to keep your laces tight. That means re-tightening your laces after your warm up, and likely at least once more during play.
A good replacement insole supports your body weight over the entire surface or the sole of the foot. It helps prevent your foot sliding in the shoe. I like Superfeet Orange because besides the support, there is an extra cushion for the balls of the feet, and the textured surface helps prevent socks from sliding.
You've got to cut your nails ridiculously short if you are a tennis player. You've got to cut them at least once a week - I inspect them more often and give them a trim as needed.