On the rear of a countryman NOTHING. I could sell them to you but you wouldn't notice enough difference if any to make it worth it.

And if you did want to do bushings in the rear the trailing arm bushings will give you the most gain as they will reduce toe change mid corner.

The rear sway bar will by far be the best suspension bang for the buck. Being stiffer it will reduce body roll a lot. But this will also give you more neutral handling just like a standard hardtop MINI.

 

I'm on my 3rd Mini, 1st Countryman. I know what I like and how how I want the car to look and handle and learned most about the latter on sites like this. I tend to buy performance items from vendors that develop and use their products themselves.....I have a Way sway based on that criteria....not saying it's better or worse....candidly if they changed it out to all of those mentioned....I'd probably wouldn't know the difference. The point here is that any will work, and your countryman will drive very differently....GO FOR IT!!!