Replacement padding

Ditto what Clancy said.  However, don't leave out the "horsehair".  If you do you'll be replacing the padding again in about a year.  The purpose of the horsehair is to protect the foam padding from being worn through by the springs which have corners and points which will wear through the foam in no time.  The burlap keeps the horsehair in position above the springs.  Some guys (and shops) used to do a quickey job by just putting new seatcovers over the old ones after stuffing any holes with rags.  You should do it the right way.  TMI makes and pre cuts all the materials you need to do the job right.  The most important part of the job is to repair the springs.  After you've taken off the old covers and padding you'll see lots of places on the springs that are broken or out of alignment.  I've repaired broken springs by using a 2" piece of steel brake tubing, bent to match the curve of the spring and then pushing the two ends of the spring 1" into the tubing.  A few crimps with linesmans pliers locks it in place.  I replace missing clips with several turns of .032" stainless tie wire.  Painting the springs is a good idea too.  If you can sandblast them clean first do it, otherwise prime them with a good rust covering/inhibiting primer and then with any good paint.  Then cover with burlap held on with hog rings.  Then the horsehair also held on with hog rings.  Then the foam padding which can be held in place with spray glue.  If you use pre-cut and pre-formed foam the coverrs should slip on with little problem.  I used bulk faom trimmed into shape using an electric carving knife.  Sometimes it's difficult to get the new covers over the faom, especially on the seat backs.  You can simply use thin plastic cut from trash bags over the foam.  The covers will then readily slide on.  You can leave the plastic in place or reach in and pull most of it out if you don't want it there.  Important - when you remove your old covers, you'll find places where there is a steel wire inserted into a pocket sewn along the edge of the cover.  Don't discard those wires as you'll need them for your new covers.  Their purpose is to provide a point where you can use hog rings to attach the new covers to the springs.  This all sounds daunting but it is actually quite simple once you get into it.  As you can see, you'll need a good many hog rings, at least 100.  You'll also need special hog ring pliers to lock them down.  If you're doing one car one time, a cheap $2 plier will do, although it get quite uncomfortable using them after a while.  A better set might cost $10-15 but won't be as hard on your hands.  Good luck.