If you keep the factory tail pipe and DIY you will need center/offset or offset/offset depending on the muffler size. You will also need a 3" pipe and some 3" clamps. Ideally you should have a hanger welded to the muffler to help support everything.
For example the Flowmaster 50 HD center/offset, Magnaflow (22" 5x11) center/offset, Magnaflow (24",18",14" 5x8) offset/offset, Borla Pro XS (14" 4x9) offset/offset
There's direct kit available from Mufflex, they have 3 sizes depending on the sound level you want and used the Magnaflow 5x8 muffler (24",18",14")