I have a number of J frames, 2 of them are square butts, and the only satisfactory grips I have found are Herretts Detective model. For the round butt models I use either the "boot" grip that most of them come with these days, or the Pachmyr "Professional" compact, this grip leaves the backstrap open, and gives you just enough extra on the bottom to have an extra finger grab space. I also use them on K/L frames that are to be carried concealed. IMHO these are some of the best grips made for real work with a handgun, they will not slip when wet, and are quite "grippy". Some do not like them because they are not as smooth as wood grips and will "grab" a covering garment, if you have this problem, again IMHO, you need to reevaluate your CC methods. I have been carrying professionally for 40+ years, and have used these grips for most of that time, they also make an OK semi auto grip, but for them I like the "thin" grips for the 1911 or BHP available from Brownells or Herretts.
BTW favorite J frames are the 940 and 442, or a slicked up 60 (bobbed hammer, DAO).