Find a good chiropractor and have the chiropractor put your wrists back in joint. You will be amazed at how your fingers will feel immediately after the adjustment. Not stiff at all and you may not have even noticed the stiffness, but you will feel the difference after the adjustments. Does not hurt at all, so nothing to be concerned about there. Chiropractors can also fixed carpel tunnel and help arthritis if that is the case.
I'm a Graphic Designer too and my biggest fear is loosing the ability to use my hands! Have you gone to your doctor? It could be anything. He/she could run a few simple blood tests to rule out arthritis and if it's carpal tunnel, may be able to prescribe you a splint. My uneducated guess is since it's only the one wrist, it may just be a tendonitis due to the angle you're force to keep it during work. You could try getting a splint from a drug store and seeing if that helps too.
Best of luck!
D.