* For myself * I continue to indulge my fetish for 2in RB K frames . To fit your stated criteria , a Ruger SP101 , preferably in 3in if belt/ IWB carried. But I suspect you were intending .357Sig , rather than wheelguns.
There are dozen plus guns that would meet the criteria , and you'd have to fondle & shoot a bunch to decide what suits you.
However , you can work backwards from what you already like and shoot well.. You like .45acp, you like your G21 , but want thinner , and shorter butt. Vola ! Two options. This past weekend I was able to try out a G36 , and was favorably impressed. I own a G29sf , and other than cal , is dimentionally identical the the G30sf in .45acp . The hybred model w/ 36 slide on 30 frame is currently all the rage in gun 'zine writeups and Glock press releases , but I don't find the standard G29/30 slide to be objectionable. So it comes down to slimness of grip vs capacity. The G36 does have a slightly extended mag that holds extra 2rds , and allows the pinkie to fit on the gun. Likewise the G30 will accept G21 mags.