Peter got there just before me! I was about to reply much along the same lines, anything that takes the concentration away from the sights such as the mirror idea and the laser dot is likely to cause a problem rather than help, just concentrate on the sights and maintaining that sight picture through the trigger release.
If you wish to train for a steady hold that is a completely different issue, but it will be irrelavent unless the sight picture is held correctly through a good trigger release and that is where the most advantage can be gained from training.
As also being another returning old fart, I am constantly surprised at how wobbly (not choice, but because of old muscles!) my hold can be and yet I can shoot good scores as long as the sight picture and release is good.
As I said "Successfull Pistol Shooting" by Frank and Paul Leatherdale is a good foundation and development pistol shooting book.
best regards and good shooting,
Robin