I had to smile when I read your question, Jeanne, because even now there are days when my fingers and hands still become sore and sometimes swollen. If I have not worked with wire for a few days, or if I have been working for 6 or 7 days in a row, 8 to 10 hours a day, my digits still become overworked.
Yes, holding the wire tightly while straightening can cramp your non-dominant hand; some folks place that end of the wire in a vise to hold it while straightening. The dominant hand that you use to straighten the wire shouldn’t become too sore if you are not “white knuckling” the wire to straighten it, as your fingers should only be countering the curve, not trying to “pull” the wire straight. If you have developed good straightening skills, use a polishing cloth while straightening the wire, which will offer a cushion for your fingers while cleaning the wire as you straighten it.
With time, you will develop thin calluses that will help to protect your fingers. To relax your hands, try a paraffin wax hand spa.
Answer contributed by Dale “Cougar” Armstrong