The best place to start is a bike fitting from a fitting pro. Though there are some excellent fitters who can solve your problems without formal training, and increasing number of fitters use a systematic approach to bike fit. Our favorite approach starts with the Fit Kit system, which uses both skeletal as well as soft tissue (flexibility, etc) measurements to establish a starting fit. Then the fitter fine tunes your position, either on a bike mounted on a wind trainer (maybe your existing bike) or a bike sizing machine like the Waterford Fitmaster (http://fitmaster.net
). This gives you a chance to try out your fit before you buy, or to help determine adjustments to your current bike. A good fitter will observe many common problems without you spending hours on a bike.
Changing your fit is much of, but not all the answer to your comfort related problems. If you have health problems, you may need the help of a physical therapist or similar professional. If you are truly new to cycling, you do have to break your body in to the rigors of long-distance cycling. A good fitter can help coach you on this, as well.
Once you have your ideal fit established, it's pretty straightforward to see whether or not you need a made to measure Gunnar.