get this bass, or the newer version:
I've never played a BG that sounds more like a double bass than this one (of course, there are still big differences). You could dampen the strings a bit if you wanted, but it's already got a very woody tone from the hollow body, wood bridge, and piezo pickup. Awesome bass. They go pretty cheap used too, I got mine for about $400 CAD.
By the way, I haven't tried flats on it yet. It'll probably come even closer, but yeah, theres nothing like playing an actual double bass.