20ga is perfect.....and kind of your only option really, you can get a 28ga or a 410 but those really step down in power....

May consider a semi-auto.......if kick worries you, not certain but I would suspect semi-auto's kick less? also just use lighter loads in a 20ga 2 3/4" etc....

20ga is more versatile than a 28 or 410 IMO too, so probably a better start.

Can always consider a 28ga, though I think performance it is very close to a 410, not sure which ammo costs more either, I know both are more than 20ga......