If you're doing sensitive analog stuff, you would want to follow the output of the switcher with an analog regulator to clean the ripple up. Switchers can have 100mV of ripple (or more) which is not really good if you want to measure uV! There's no reason why you can't cook up a small converter -there's plenty of circuits on the web. Some circuits don't even have an ic - in fact you could build one with one transistor (and a handful of passive parts) - just don't expect it to be regulated! Personally, for a commercial product I just buy one 'off the shelf' as you can spend a lot of time trying to make a converter reliable as well as CE compliant. For a hobby project, it's always educational to build one for the experience.