Do not underestimate the value of shipping discounts. There are plenty of perfect gifts that are just out of reach of travel for many people, which makes shipping their primary delivery method. Offering shipping discounts during the holidays lets you compete with the big boys like Amazon without crippling the rest of the year's revenue.
If you're having trouble crunching the math, so you come out ahead with free or discounted shipping, you can always set a minimum purchase amount. Alternatively, you can offer it for your lighter items.
Years are long, and there are plenty of holidays to take advantage of. If you're looking to give your business a boost, target one and make a marketing campaign revolving around it. Do it soon; the earlier you start planning, the better things will come out.