I have done double bocks a couple different ways.
1. Lots of Pilsner (or if you are a cheap bastard like me, American two row) and caramel malts. This is how Sam Adams does theirs, just two-row and Crystal 60.
2. A Munich-based recipe with some darker malts for complexity (Carafa, dark munich, crystal 120, etc.) and some Pilsner (or two row) to help fully convert some of the more highly kilned malts.
Of the two I preferred the latter.
They age extremely well so do yourself a favor and put it away for a year after it's done.
My favorite recipe used C120, C60, Caramunich, Melanoidin, Gambrinus honey malt, two-row, and a bunch of Munich. Turned out fantastic, bread and chocolate and plum flavors among others.
Also: decoction mash.