Some ammo manufacturers recommend using an IC choke when shooting slugs through a smooth bore barrel, but MOD should work too.
I've bought Carlson's and Trulock chokes in the past and don't find one to be better than the other. Carlson's are less expensive though.
also offers a rifled choke tube (sort of a poor man's alternative to a rifled barrel). I've heard it doesn't work well for fast sabot slugs, but that it can stabilize Winchester BRI sabots and some of the slower Lightfield offerings. Also, Remington's Buckhammer slugs are specifically labelled as being intended for "rifled barrels or rifled chokes." And Brenneke claims that their rifled slugs are often a little more accurate through a rifled choke than through a regular choke.
As other have recommended, try a few different brands of ammo and see what works best.
If you really want to stretch the distance toward 100 yards, I'd look into some of Brenneke's offerings, such as their Green Lightning load.