@airbiscuit
Yes, I purchased a suspension seat. It helps minimize the back pain, but it by no means is a miracle. It is a temporary fix. I also air down the machine's tires. Again, less tire pressure makes the ride a little softer, but it's a temporary fix.
I have been mowing less "lawn" this season simply because of the rough ride. In my opinion, the area has not been less rough with the grass, weeds, clovers growing in. Repeated mowings going in various directions has not seemed to improve much either. My neighbor has mowed areas and agrees it's not pleasant using a zero turn. Purchasing a large tractor with various attachments to try to get it solved is not financially possible at this time.
Filling in spots with topsoil/sand seems to be a good idea. It will take a lot of time, effort, and money to get all the acreage covered. This might be a multiple year task to accomplish.
I hope I didn't come across as unappreciative to anyone who contributed to this thread. I truly appreciate everyone's input. I will for sure pass the suggestions in this thread to the farmer and see what he things would provide the best outcome.
At this point, the option of having the farmer that did the work come out with his machinery and big roller seems to be what will happen, unless he has a different plan.