There is a company Seat Comfort Systems that sells carbon fibre elements instead of the wire types. These can be cut (lengthwise only) to fit your specific seat. I'm thinking of using this type so I'll never have to deal with broken wires again. Check them out.

I replaced mine last winter. I got the part from Tasca Volvo in MA. You can get it from any mailorder parts department- Borton, Volvo of Houston, etc. There are names in the back of the car mags and you can save around 20%. I paid around $50-55 for the part. To remove the seat cover, you have to cut the hog rings with a good set of cutters. I got mine from Sears. You have to cut enough to peel back the bottom seat cover. Once that is done, you have to remove the old element without taking too much of the seat foam with it as it is glued to the seat. Once removed, put the new one in place and start reassembling the seat cover. I used small zip ties instead of hog rings. Good luck.