You appear to be groping your way through. Sounds familiar. I'm no expert on power supplies, so I don't know how much stability is improved by a switching supply. Fortunately, they are pretty easy to set up (though not as easy as a linear regulator). On the national semiconductor webpage, you can find a web-based and a downloadable tool for designing a power supply. Both with present you with various options and output a parts list and a circuit diagram for you. By the way, most of the components are available as free samples.

Can you get over the wobble in the Vrefs by sampling over a longer period, or by averaging lots of ADC readings?