I have had a Specter Gear
CQB 3-point sling on my 870 for quite some time and it is really comfortable and sturdy. It came with a
GG&G front sling adapter, which is secured by the magazine tube cap or magazine extension. The GG&G front sling mount is the sturdiest front sling mount I have ever come across, and because it comes out the side it allows the gun to rest more comfortably and more securely against the body. The rear mount for the sling wraps around the butt-stock. The number of configurations you can have the 3-point sling in, makes it the most
versatile for carrying your 870 around in the bush.
If you are more interested in a single-point sling,
S&J Hardware makes a very nice single point sling mount.
When I find the 3-point sling too cumbersome, and want a bit more freedom of movement with the gun, I opt for a Specter Gear MOUT single-point sling. It attaches to the gun with a GG&G
single-point sling mount that allows me to use an
HK clip to attach the sling to the gun. The HK clip attaches and detaches quickly, but won't ever let go; I also have the option to use a quick release buckle with the MOUT sling.
Although the gun is more easily accessible with the single-point sling, the gun tends to swing around a lot.
A heavy duty 3-point sling would probably be more comfortable for the needs you're describing. I only have experience with Specter Gear slings and Spec Ops slings. Of the two, I would recommend Specter Gear.