Go to a 3x3 spot of flat bedrock in the top of the nether, place a piston 4 blocks below the center block in that square, and a lever in front of it. Make the wither formation on top of the unexpressed piston, and a wither should spawn. Immediately hit the lever so the piston extends and the wither's head is in the ceiling. Then pull out a wood Sword, or any sword and just kill it. It cannot hurt you.
Yes, dig a staircase mine then dig forward in the wastelands or wild, then build the wither in a small dug out room at the end of the tunnel. Have decent armor just in case along with a good sword and bow.
