I have been practicing for years with very light 38 specials, and they are fun, and cheap. I have fired a many a wheel weight down range in hideout pistols. Not uncomfortable at all to shoot. Lighten up your practice load and enjoy. The whole idea and concept of practice is to develop "muscle memory" with the weapon, and conscious, and subconscious gratification to become confident, and competent with it.
When you walk out into the world with it, stoke it with "business rounds". I can't however imagine going lighter than an aluminum receiver. There is a point of diminishing returns, where a weapons is so light, it becomes a burden to shoot regardless of the load. I have never really cared for aluminum framed handguns, yet in 1978 used one (custom light weight Commander). My Model 60 is an all stainless revolver, and I never notice the weight in carrying, but appreciate it's strength in construction.