there are a lot of threads on reworking the existing seats...pool noodles. Just finished this project in my 300TD, ditched the horsehair pads and covered the springs with heavy canvas, two layers of 1" foam, plumped up the side bolsters with foam strips, and pool noodled the springs. It was worth the time, effort, and money....seats feel and look much, much better. May sound crazy, but now that seat is comfortable, the car seems to handle better...actually it just that I am up higher in seat and no longer wallowing around behind the wheel.
I got my covers from
www.hirschauto.com , then there's ebay, junk yards, and other suppliers where a cheaper deal may be found. the hirsch covers were very well made and installed real easy.
Life is too short to ride around with a spring stuck up your butt!