Felt very little support in the bottom foam of my base seat. Found a similar thread in a search that discusses the issue and suggested a solution, but did not have photos.
http://986forum.com/forums/general-discussions/27464-sagging-drivers-seat.html
Here are some photos of my repair. First some details, in my situation, there is a belt of material that supports the foam. That belt had split allowing the foam to sink lower than it should.
Using a hole punch I made a row of six holes on each side of the break in the belt. Then using zip ties (no, not duct tape....

) pulled the belt back together. For added support, again using zip ties, created a loop going from side to side. Of course I was worried that the zip ties would just pull though the belt material, but so far so good. Now, when I get in the car, I do so gingerly. Only 185lbs, but I used to just drop into the seat.
Hope this helps the next guy.
Good luck, Joe