Just purchased my 4th Mini (15 R60 JCW)....exactly what I wanted and exactly what I expected (only 1 disappointment)...love the look of the lounge seat...and I don't drive all that aggressive but the side bolsters don't hold me in like the sport seats....I'm going to my local "magician" who customizes interiors except I like what I have and all I want him to improve is potentially increasing side bolsters within the existing pattern....Mission Impossible for sure but if anyone can do it he can..will keep you updated. If anyone has been to the promised land and figured this out...please save...Thanks!

 

This video is for a WRX, but maybe it can be applied to your seats.
I have a WRX and performed this mod to my front seats. It's a great improvement compared to how they came from the factory. I also added some foam to the lumbar region since my WRX's seats were lacking there, too.

I hope this helps! Good luck!

(not my video, btw. a buddy of mine gave me a link.)

 

Thank you!!