I know you are looking at ergonomics, but to me, I want to compare apples to apples. That is, stay within the same caliber. And that's where the R9 has them all beat! Ever since I read about the pup in AMERICAN HANDGUNNER magazine a few years back I knew I had to have one. I was just looking for the opportunity. I finally saw one at a gun show a few weeks ago and jumped on it.
I've always carried the smallest with the largest caliber ratio gun-wise. For example, when Kel-Tec came out with their 380, I quit carrying their 32 when wearing jeans and went to the 380 for my "jeans" gun.
But back to the subject. To me if you have to stay with a 9mm, the closest would be a Colt Pocket 9 . Very ergonomically similar, but larger. I have one that my gunsmith shaved off enough weight to give me the equivalent of the free mag with ammo(weight wise) It works very well for pocket carry. Unfortunately, they are not made anymore.
Next, I would pick the Kel- Tec P-11. Double action, 9mm, eronomicly similar, lightweight. Drawback, a little thick for front pocket carry of jeans unless very loose. I used mine in front pocket of dress slacks with Kim Ahrends Natural holster. Conceals, very well. Even got pulled over by an anti-gun state trooper for speeding and was asked to get out of the car, when I told her I was carrying, she asked multiple times " WHERE was I packing a nine?"
Oh but now, I have the Holy Grail!, the R9! No more searching needed.
Unless I need one for my left pocket, or maybe a backup, or............
Reinz