Keep in mind that using a saddle that is too big can be just as detrimental as using a saddle that is too small. I just went through this with my own horse and no matter how thick a pad I used it just wasn't able to compensate for a correctly fitting saddle. Saddles that are too big can rock around and create uneven pressure. Just eyeing him, it doesn't look like he'll ever need full bars, but again that's just by eyeing him. As mls said, try to find a saddle fitter in your area and that'll be your best bet. Not to nit pick but where is your cinch sitting on the off side? Is it sitting as high as it is on the on side? If so, I would suggest buying a smaller cinch. If not, I would suggest moving the cinch higher up on the off billet.
Everyone has given you good ideas on fitting already, as far as checking the saddle while it is on a horse you want to run your hand in between the horse and the saddle. Make sure you can run your hand through and that there is fairly even pressure throughout. If there is a spot with more pressure or you have to force your hand through- something is pinching. If everything seems like it is fitting fairly evenly, take it for a spin and see how your horse rides out in it.
Also your horse doesn't look swayed to me. Right now he looks to be downhill and that is what it probably causing him to look like he has a bit of a sway. Once he shoots up in the front end, he'll probably look a lot more balanced and evened out.