I'll second the BPS fluoro as being good. If you can find it on sale, pick some up. I've heard stories of people casting lures off the "vanish" line. I guess it's not just the line itself that vanishes, but also lures tied to it
10#/12# is pretty reasonable for crankbaits if you really need to get down there. Just set your drag and play the fish accordingly. And keep checking the first few feet of line for kinks and notches.
If you're not needing to hit 15-20 feet, you can probably upsize your line a bit. Just fish a crank that runs a bit deeper than you think it needs to (e.g. run a 12 ft diver in 8-9 feet of water). If you're not hitting bottom, use the next deeper diver.