I stumbled upon, researched, took on and completed the Side Bolster Mod to my standard leather seats. It was fairly easy, apart from reattaching the seat back, which was a pain, but was sorted in the end. The difference is night and day. My standard seats don't really look any different, but they now hold me in on the corners and are more comfortable than before. I added some padding back in to the sides to help fill the new gap at the sides of the seat back cover.
I'd say that the seats feel how I expected them to, much more like the ones in my old Audi, and more like you would expect in a sports car.
It's a good free mod if you have standard seats, and slide about in them too much!