I'd suggest using real, fair-trade, organic sugar. Your body knows what to do with sugar (unlike those artificial chemical sweeteners), and if you are really just having one cup of coffee a day, it seems like you probably wouldn't waste too many points with real sugar...unless you use a LOT, in which case cutting down is probably a good idea.

My experience with weight watchers is that those 'extra' weekly points are for things just like this - sugar in your tea/coffee, a glass of wine, or a bite of chocolate. If you really enjoy that coffee then it is worth a point or two. I don't have any experience with stevia, but all of the artificial sweeteners are really things to avoid.