Reupholstering and getting it right is expensive. Depending on where you live, junkyards are a possible source, but it might take some time to find a seat in good condition.
I have a torn up driver's seat in my '93. The foam in the seat pan and bolsters is still pretty good, so I'm going to tape up the tears in the seat pan and buy a seat cover from IPD. IPD sells all the main parts for seats--new foam, covers and lumbar support.
John "Baloney" Clay
1993 Volvo 240 Wagon