I'm looking to replace the Body Geometry Toupé Sport, 143mm saddle on my 2016 Specialized Roubaix. Sit bones measure approximately 133 mm apart. What size saddle would be most appropriate? This 143mm is apparently too small, as rides over 10 miles or so haven't been very comfortable. I get a bit of relief by sliding way back on the saddle, but I'm obviously too far back.

Also wondering if I need more of a flat type saddle or rounded one? I'm thinking about trying a Power Expert or Phenom Expert saddle. I realize it's gonna be a trial and error process, but any and all experiences and opinions are greatly appreciated.