Personally, I was unable to wear IWB holsters because they just hit me wrong and began hurting after a few minutes. I called several custom makers until I happened upon Ken Null's UNS that is shaped like a rectangle with a radical rake. Extreme comfort and easily the fastest holster I own bar none. I use mine with the Colt Lightweight Commander. Mr. Null's work is second to none and he can answer all of your questions about carrying concealed where many holstermakers cannot.
If you prefer Milt Sparks stuff, the EX Executive appears to be similar, but I have no personal experience with it.