Before doing an accessory buying -make sure your towing setup is correct.
Trailer frame needs to be level (parallel) to ground when hitched/loaded. Don't eye ball it -measure the main frame near rear and in front before the frame step up. Proper setup has these numbers nearly identical. My personal limit is one inch maximum difference with front being higher than rear. You ask why only an inch - because additional front height compromises suspension travel which amplifies the issue you are having now.
The next most important thing before investing in a cushioned pin box or hitch is Pin Weight. From my experience, which pretty much mirrors rhagfo above, is that as a percentage -Pin Weight needs to be around 20% of actual loaded trailer weight for the best ride.
A third thing is concerning the factory overload engagement. IS it staying fully engaged or fully disengaged? If spring is bouncing off overloads -the ride suffers greatly
I am a firm believer in having real shock absorbers on the trailer axles, too. They just calm the trailer down by getting rid of the sharp impacts.
Good luck!
Use Gross Axle Weight Rating when determining loads being acceptable or not. A trip to the scale is a very good idea -that way you know what the weights are exactly. You only tow "dry" one time on the trip home from buying the trailer.