I don’t want to change the gun but wondered if a lighter load would help.
Can you recommend anything? Are sub-sonic cartridges any good for decoying or do they lack knock-down power?
A 1oz trap load can still be quite lively, particularly from a light side by side.
Sub-sonics can be effective once you get used to them, but if you shoot normal shells for other disciplines, you will get into an almighty mess with your sight pictures.
If I were you I would try a few different 21 gm loads of which there are plenty to choose from.
Provided you cut back on taking 50 yard “gallery” shots you should find the recoil is negligible and they will still be effective out to 40 yards.