It sounds like you are doing fine so far. Just go back to the saddle, and get it tightened and let him figure it out. Or as some have suggested, put a syrcingle on him, as that will give him the sensation of a girth, but is quicker and easier to tighten.
You can also put a cotton lead lightly around his belly and tighten, loosen, tighten, loosen; and do that until he relaxes. This gets him used to the sensation of something around his girth. This is how I prep a horse for a girth; you are safe from flailing legs, as you aren't reaching under the horse for the cinch. Once you do get the saddle, or syrcingle on, longe, or round pen him until he stops bucking or otherwise relaxes.