see if you can get a complete seat at the scrap yard and swap the cover...or get new covers to put over the old if that bad...
auto shops may be in your area that do interior work like this...swaping the covers....
your weight over time causes cracks in the metal ...a used seat given the age of your vehicle would be a smart way to resolve this...
the auto makers should make stronger seats for the big guys ...should be an option ..
these vehicles may have not changed the seat structure so may be a newer model will fit ...the scrap yard guys should know.....