Having recovered from terrible wrist tendinitis, I advocate resting using a quality chair with adjustable, padded armrests and resting your forearm (just in front of the elbow works for me) on them. Having them slide in and out so your elbow is tucked in near your body is critical for comfort, in my experience.

My favorite chair so far is still the Steelcase Criterion.

Trying to support your arms while typing would create tremendous tension in your shoulders. I was always confused by the classic typist advice to have no arm rests.