The mantra is to get fit to find the best combination of head and shaft for you. A 12 handicap is within a range that one could justify any Titleist iron. The one question is about the one-length irons. It would take a lot of customization to fit Titleist heads to try to make a one-length set. If you are a true fan, it might be best to keep your current set. Not many options for 1 length in the marketplace.

As long as you are comfortable in giving up the one length concept I am sure you could be fit in almost any of the Titleist clubs as suggested by Don- a fitting would be very beneficial in securing a satisfactory switch. The one length clubs require heads of the same weight throughout set and Titleist are not going to be able to meet this requirement unless they decide to design their own one length line. I wouldn't sell your one length set until you have some time using your new Titleist set, but, am confident you won't go back.