For front suspension, I installed Progressive fork springs, added a fork brace, and used 15wt fork oil. For the rear, a set of 13-1/4" FXDX shocks with progressive springs and adjustable rebound damping. I weigh about 200, and the shocks are fine on the loewst preload setting, leaving plenty of adjustment for a passenger.
Two on my bike (with the 2-up seat lictured here) are kind of cramped, but not bad for shorter distances. The low bars help, too.