We might as well get the back seats out of the way. The back seats are done pretty much the same way as the front seats. Start with a box and shape it into the basic shape of the rear seat cushion.
Now just do some shaping and tweaking to get it rounder. Make the rour ridges in the same way that you did the front seat ridges by extruding. Cut in any edges that you deem necessary. Make sure you shape it so that it fits in the space in the back seat area. Also make the lines a little crooked and natural looking by randomly adjusting vertices. Extrude out the section shown in the picture.
Mirror the cushion across to the other side and adjust it so it's not perfectly identical to the other one. When smoothed, they should look something like the picture.
The top half of this chair is pretty much made the same way, create a box, shape the box, extrude the ridges, mirror a copy, adjust vertices etc. Surely you get the hang of it by now so I'm not going to go through it step by step in this case. I will just show the finished product and you should have no problem creating the same thing.
Things are progressing very nicely on the interior. Let's now add the gear stick. This is extremely easy to make. We will once again use a spline to make the base of the gear stick. So, draw the shape shown using the line shape tool.