whiteline, or powerflex uprated bushes
whiteline do a rear one, i tested it for performance tuner magazine, worked well but was way too much on the hardest setting, the car just went sideways
Why not start with doing harder bushes, solid top mounts and a non adjustable strut brace first. See what improvement is felt, then see if you need a stiffer bar. Might feel a lot sharper on turn in this way and you may not even need a stiffer bar.