I have done mine [ E320] and although there is nothing really hard /complicated , it does require seat removal
from the car. The complete job will take up most of a day
and a lifting helper is nice. The seat is heavy and lots of wiring and plugs to tend to.
The tie downs for the cushion rods require a tool , but one can be fastened from a coat hanger w/hook on the end.
If you are not handy, I would get the new cusion and send it out to a trim shop.