You'll be surprised by how a properly fitted ball will feel in your hand. My wife and I joined our first league earlier this year, and we both got our own balls a few months before league started so that we could get some good practice in before our league started. Like you, I'd been using house equipment and I was scared to move up in weight since I always threw 12 pound balls. I could tell that the pro I was talking with really wanted to put me in a 14 pound ball, but he could sense my hesitation and ordered a 13 pounder for me. It was more than apparent in the first game that I threw that I could have gone with a heavier ball right off the bat. I've since moved up to a 15 pound ball, but I recently picked up a 14 pound spare ball and I really like that weight. I'm seriously considering getting a 14 pound ball when I make my next hook-ball purchase.
My recommendation, given that I feel I've just traveled the road your about to travel, would be to go ahead and get a 14 pound ball and have it drilled for fingertip grips. If you're serious about your bowling, you'll eventually want to move to fingertips anyway and the transition is an easy one. Also, like you, I work with computers a lot at my job, and I experience some wrist pain due to the early stages of carpal tunnel syndrome. I highly recommend a wrist brace of some type. I have three: a Storm Gadget XF, a Robby's Revs II, and a Robby's Cool-Max. Out of the three, my favorite is the Cool-Max. The other two change my span too much and I have trouble holding the ball with them on sometimes. The Cool-Max is also the cheapest and most proshops will have them in stock.
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