Without a doubt I would get D'Addario Chromes. They are not ridiculously expensive and while they take a little while to break in and get past some of the initial brightness, once you do you'll never want another set of strings. I would suggest getting the lightest gauge, the ECB80 set, which is .40 - .95. It sounds really light but these are thick strings. I've found that higher gauges of flats are too stiff for me, and I don't like that they are high tension and pull on the neck.
You can check them out here:
http://www.amazon.com/DAddario-Bass-...584981&sr=8-10
Amazon is actually the cheapest price I've seen, believe it or not. Plus, if you're like me and you buy a lot of stuff on Amazon and have the Prime membership then I think that shipping is free. Even with shipping I think we're talking about $30 or so. I looked for years for flats I like and these are far and away the best I've come across.