You'll never find ammo in 16 gauge, at least not easily.
I have an 870 express with two barrels. a 28" with removable choke and a cut down 19".
The felt recoil from the two barrels is night and day. The longer barrel makes shooting 00 buck tolerable for a longish practice session.
But I don't often want to shoot more than a dozen from the 19" barrel.
As Carl mentions, you can now find 12ga buck in reduce recoil flavors. This does help. You can also drop down to #4 shot. It's all trade offs.
20ga will be easier still, but you're sending less payload down range for a given shot size compared to 12ga.
That all said, maybe it should hurt (me) a little to unleash so much awesome power.