Personal preference really. Odds are if you have had your pool for awhile and using bleach, your salt level is well above zero ... maybe in the 1000ppm range.
SWG generally require 3000-3500ppm of salt, but I have read posts here about people adding salt up to 2000-2500ppm without a SWG just for the "better feel". Note that the ocean is around 35,000ppm.
There are a few things to consider. The salt water may be a little harder on metal around your pool and some natural stones (coping etc) could be damaged by the salt.
If you want to add salt, it is as easy as buying a few 40 lb bags (look for Solar Salt at HD/Lowes/etc which is about half the price of "pool salt"), dumping them in the pool, and brushing the salt around a bit until it dissolves (usually within 10 minutes from my experience).
EDIT: For your pool, each 40lb bag will raise the salt by about 250ppm. And each bag costs about $5.