When sighting in a shotgun, a bench and sandbags are great; however, for practicing your shooting you should do it from a position that is similar to what you will encounter when turkey hunting. For lots of people that is on low-boy stool or even sitting on the ground.
When you are doing the bench shooting you can put a small sandbag between your shoulder and the gun. I do this with my 300 magnum sometimes, and it keeps you from getting punished. Also, a good slip on pad will help take the bite out, and you can use one of those from a bench and hunting too.
Here is an artice that is a bit out-dated, but you might enjoy reading it anyway:
Now that you have developed a flinch, put the punisher away for a few days and do some shooting with a 22 rifle - you will soon get rid of the flinch. When you start back with the shotgun, build up gradually, use a pad, and don't shoot too much at any one time.
Good Luck with your shooting,