To get more comfort along with some pop from a racquet, I'd say you ought to try some stuff with some degree of flex along with some significant heft. That might not be so great if you like to "whup" on the ball with more racquet speed, but there's the upside of the greater measure of arm-friendliness, etc. along with the extra plow-through.
While I agree that the Redondo is a very cozy frame, I didn't get the gas out of mine that I wanted when compared with my Volkl C10's. For a "soft" racquet, I'm still amazed with the overall performance I enjoy with the C10. Plenty of spin and power for me, but no arm irritation when keeping a heavy schedule - and I hit a full one-handed backhand.
Even if your build is rather slight, you should be able to learn to use the swing timing you need to get the strings to the ball with a heavier option. Remember that if your arm feels tired on the courts, that only means that you're neglecting to fire things up with your big, strong legs.