If you find a upholstery shop in your area, see if they can order the
original style carpet.  I did a 72' 115 (220 gas) and it had the same
problems where the inner rocker carpets were bad.  The replacement was
identical to the original but it was expensive.  You will just need to
make sure you get enough length to run the entire length since the
width of the carpet usually is smaller than you would need for
something like this.  When I did mine I also re-covered the rear deck
with the left-over.

Regarding the seats, the bottoms are usually held on to the seat frame
with hog hooks.  I know of people that have ordered replacement horse
hair seat pads if that is the style you have.  Something I did for a
friends 450SLC was to take high density upholstery foam and using a
electric kitchen knife, cut the foam down to form the same shape as
the original pad.  If you are careful you can re-use the hog hooks
when you stick it back together.  One thing to be careful of is that
seat pleats are sown to a backer canvas.  If this stitching is week
you may end up making more work for yourself as you do the pad
replacement.  If you tackle the seats yourself, plan a good day or two
to do it since it involves removing the seats and doing some
disassembly on them just to get started.

Regarding the back seat upper, you will need to stitch in a
replacement backer that holds the seat material tight.

Hope that helps and good luck.

You might try a wrecking yard. I see lots of these cars for parts near me.
Craiglist also. You can pull parts off a passenger seat to use for your
drivers seat. The seats on my 85 were really easy to work on, no hog hooks
to deal with.

Since it was wet you may have a problem getting the seats out. The bolts
that hold the seats in may be rusted tight to the nut. If so you'll have to
drill the head off. The nut is held to a sheet metal bracket. You can get a
replacement at the wrecking yard.

Everything you need at   http://www.performanceproducts4benz.com

Not cheap, but creates a new interior.