Really easy project to do. I just did my Ram a few nights ago. I had the same thing, stiff right side and broken down on the left. I sat at a bit of an angle because of it and it drove me NUTS!!! It also hurt my legs after awhile.
Just pull the seat out, pull back the cover and either add foam you've custom cut to do the bolster etc...which is what I did. OR, you can typically find full replacement foam on ebay etc that is OEM. I used the replacement cushions you can buy at craft stores for patio furniture or boat throwables and trimmed accordingly. Took a total of 40 minutes and I had the seat back in and bolted in the truck.