I would go with KYB exel Gs at £53 each on the rear (damping rates are higher on these over standard), add some custom springs from springcoil spec'd slightly higher rate than standard & dropped 25-35mm at most. custom springs front & rear would probably be around £230. It will be all new, vehicle will sit right without hassle & it will handle far better.
You will notice a night & day difference with just bad SLS removed so adding cutsom spec springs improves things a little more, done the odd XT with springcoil sourced springs & always been impressed with end results.