There is little doubt that the easiest way to change your seat cushion is to change the whole seat (5 bolts, one snap connector - job done) and this could even be the most economical solution too if you stay close enough to the seat supplier that you can call and collect.
I've taken a different route with my driver's seat and for all sorts of reasons too tedious to go into here decided to replace the cushion cover. Just in case someone else is similarly minded I've posted some photos of how to do it below.
David wrote a great guide to seat removal here:
http://www.the-t-bar.com/forum/21-aiketgates-guides/16681-the-seats-how-to-remove-and-refit
(NB do disconnect the battery first for 20 minutes to remove the risk of the pre-tensioner firing).
His guide here on how to dismantle the seat and remove covers is equally useful and is here:
http://www.the-t-bar.com/forum/21-david-aiketgates-guides/16625-heated-seats-how-to-fit-heat-pads
So now for my bit - the fitting of a new cushion cover. You will need at least 16 cable ties, a couple of pairs of long nosed pliers, a small pointed knife and some side cutters (and a new cover of course).
The old cover is all that holds the foam to the seat frame so it's easy to have a good clean around (and to fit lowering springs) when the cover is off:
There is a layer of something very like garden fleece between the foam and the base that needs to be put back in place first:
The underside of the foam has shapes in which helps it locate back in the base:
Before you put the foam back though it's worth putting your cable ties in (these will replace the hog clips). There are 5 ties needed along each side and 3 ties in each of the cross fittings (there are 2 cross fittings):
With the foam back on the base it's time to start with the cover. The cover has long plastic channels at the back, each side and the front which clip to the frame. It also has bars along each outerside and cross ways in 2 places that marry-up with the cable ties and are essential for a good shape.
Start at the back of the seat by clipping in the rear of the cover:
Fitted here:
Then work from the back of the seat to the front fitting the cable ties in pairs along the sides and the cross bars when you reach them. You will need to make a hole in the cover bar fitting for the cable tie and try to judge where the bar will be when everying is tight. To give yourself a margin for error, it's best to postion the cable tie mid-in the foam (it can slide back & forth a few mm). I found the easiest way was to use a small and pointed knife to make the hole and guide the tie:
Feed the ties through as a pair left and right and when both are threaded, pull tight, cut off the excess and push the joint back in to the foam:
To be continued......