I'm wondering why you "need another shotgun." Got one already? It'll probably do just fine, but any excuse for another shooter is fine by any acount.
Best advise is to get some rather hefty loads (shot, not necessarily powder) & pattern them with your prefered choke (& I agree with a full/extra-full choke). Many do good with a 2-3/4" shell with #6s, I prefer a 3", 2oz Federal Premium #4s in an extra-full - patterns wonderfully in mine - YMMV & should find out what yours does regards patterning & at what range.
Suggest doing an honest pattern on a turkey target at 40 yards & see what you come up with. Aim for the head/neck & count lethals in that area.
Far as shotguns, I think I've fired maybe a half-dozen other than 870s - a bit biased. I picked up a nifty 21" bb", double-bead w/an extra full choke 870 a while back as my turky shooter & has done all I could ask. Others will do as well (I suppose
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Far as slugs ... don't rule out the smooth-bore as an accuate shooter of the Brenneke-style slugs. I'm getting about 3" (center-to-center) 3-shot groups with PMC's 2-3/4" 1oz B-slugs (@1600fps!) at 50 yards w/an imp cylinder iron sighted bbl. Shoot a few varieties, see what your shotgun/choke like best, note the POA/POI & buy a few boxes.
Nice double-duty shooter those scatter guns ....
Camo is important, not moving is moreso. Turkeys see color, aren't birdbrains ....
CO turkey hunting is more like going after elk sometimes - wish I could try the "easy back east" birds sometime ...