Lots of good advice so far. However, before you spend any money, try adjusting the handlebars to one of the different positions. That's free, and sometimes it's the angle/rotation of the wrists that causes the numbness. I had this problem with my '04, which doesn't have the factory adjustable bars like yours does. I ended up with very short risers that also changed the angles of my wrists. This solved my issues completely.
Wanted to add that the Yamaha grips are notorious for being thin. Many FJR owners have changed to gel grips, Grip Puppies, or the BMW Sport grips. The BMW grips are ribbed with a slight palm swell and much more comfortable than the stock grips, IMHO.
p/n 32721458396 (throttle side)
p/n 32721458395 (clutch side)