If you went 20ga, keep in mind weight of the shot load and velocity equal recoil. Federal has a low recoil load, shop around some of the smaller ammo companies, salt creek, burgess creek, fox trot and look for a 1 3/8th oz load, Apex has one in 2 3/4 for sure as well.
Sub 1100 fps will be a good gauge for recoil as well.
I hand load a 1 5/8th oz load and in a light 20ga I wouldn't have a kid or small lady shooting it, it's quite stiff on recoil even in a gas semi auto!
Any TSS turkey load will get you 40yds with 9s!