The "simple" solution would be to purchase a DC/DC converter from someone like Vicor or one of their competitors. They can be purchased as single, dual, or multi-output devices, but new they're usually not cheap. DIY? Maybe, if you have the electrical engineering background to design it or the wearwithall to google a design. There should be a bunch of designs in the wild, (and many at semiconductor sites in the form of reference designs) but I can't point to one for you.