Instead of adding a metal clasp or closure to your necklace or bracelet, make a button-and-loop clasp using nylon-coated beading wire.
a) Measure your beading wire, allowing enough length for all of your beads and other components and leaving about 3" on one end to form a loop.
b) Use the beading wire to string a crimp bead and then a plastic, wood, or glass button (either through the holes or the shank of the button). Crimp or flatten the crimp bead, then string the beads in your desired pattern.
c) String a second crimp bead and then several size 11 or size 8 seed beads to form a loop large enough to fit the button through. Test the loop to see if it is big enough to accommodate the button, then add more beads if needed. String the wire back through the crimp bead and flatten.
(Note that the crimp beads will likely not come into contact with your skin if you use a larger bead on each side of the crimp beads.)
d) Alternatively, you could use a needle and thread (instead of beading wire) to form the loop by knotting the thread in between beads (make sure to pass through the beads several times to reinforce the thread).