If you are having problems with too much wrist action on your putting stroke, try switching to a belly putter. The shaft of a belly putter is several inches longer than a traditional putter. This allows you to brace the end of the shaft against your stomach and swing the club like a pendulum. Your hands and wrists cannot accidentally affect the trajectory of the swing, so your club head moves in a straight line toward the ball.
Stand in your normal putting stance with your feet shoulder-width apart and your knees slightly bent.
Place the end of the putter grip against your body so it sits about 3 inches above your waist. Adjust the putter up or down along your stomach until you are comfortable with its position. Lean forward slightly to press your body weight into the end of the shaft to anchor the putter.
Start off using your normal putting grip. If this does not feel comfortable, switch to a grip designed for use with belly putters. Place your non-dominant hand on top of the shaft with the thumb overlapping the end and the knuckles facing out. Wrap your dominant hand around the bottom of the grip with the fingers pointing toward the ground. Keep your index finger extended along the shaft to guide the path of the club.
Use your dominant hand to move the club like a pendulum and stroke the ball smoothly. Keep your non-dominant arm still so it can act as an anchor for the end of the club.