Start interchanging things side to side, start with the tyres, then pads, then discs, testing after each item has been done to see when it either pulls up straight, or the other way. The bottom link strut is more likely to have the ball joint with excess play than the rear bush doing the same. I'ts not necessarily a case of replacing everything, rather finding any faults, and then swapping bits over until you get to the thing causing the problem.
But if you get to replacing discs and calipers, I would always suggest fitting in pairs. (Although when it was for a customer they often didn't see it the same way......)