We don't have rock bass here, but I bet they would fool the crappies nicely.
If you don't like breaking thread, GSP comes in very thin diameters and is much stronger than normal thread. Unfortunately, it's also much more expensive. Kevlar and GSP are great for toothy critters where the teeth can cut thread, so I only use them on salmon/steelhead jigs. Hear they're good for pike, musky and walleye jigs too.
I lucked out at a fly tying show a few years back and found a guy selling spools of 80 and 210 denier for $0.99 each. I bought all he had left, which was about six spools in three different colors. Still have a bunch since I use 210 flat waxed or monofilament thread 99% of the time.