XDS 9. Good choice.
Nathan, you're going to have to just load by trial and error to find a load recipe that is tame, yet still able to cycle the action. If it were me, I would go with a 115gn plated or jacketed bullet and a fast powder. From my inventory of powder, I would (and do) use AA#2; but any fast powder (Bullseye, W231/HP-38, Nitro 100, VV N310, TiteGroup, etc.) would do just fine.
But before you do that - assuming it's a new piece - I recommend taking it out to the range and putting about 300 or so rounds of regular strength ammo through it, to get it broke in. IMO, in order to do a good work up (or work "down"?) of a light load, you need your gun to be broke in.