I second searching out one or more demo/loaner programs.

The correct saddle shape for you will have everything to do with the shape and width of your sit bones, realative flexibility, the way you sit on you saddle, etc. Interestingly overall width and the flesh we carry on the outside have little to do with some of those factors. I'm am in every regard a "large man". Truly "heavy framed" (not just an excuse for my weight), broad across hips and shoulders, reasonably tall at 195cm, size 51 shoe, etc. Yet, I find saddles that fit into the "medium" width range most comfortable (Selle Italia Turbo, etc).

When I recently examined if there might not be a better saddle for me I demo'ed/trialled saddles from three different LBS and was absolutely open and honest about that fact with all. I ultimately purchased from a fourth LBS who was running a sale on a saddle that the other three didn't have on hand. This, like clothing and shoe purchases is an area where LBS's can actually provide some real added value and we can support them by utilizing this fact and eventually purchasing from them for the privelege.

If you have no idea where to start, find a Bontrager or Specialized dealer. Both will have a sit bone measuring device that should help get you in the ball park. Then listen to what they have to say and perhaps visit a few of the saddle manufacturers websites that provide general selection guidelines around torso/pelvis flexibility. With that, you should have a reasonable starting point for trialing saddles. It's not uncommon to try a half dozen or more saddles before finding "the one" shape for you.

Good luck,