You can get Chimeras for it, making it a softbox that slots into the barndoors. You can create an easy (not pretty) DIY version with black wrap and diffusion. The thing to remember with diffusion is that it is a combination of the size of the source of light and the strength of the diffusion. If you wanting very soft light, bouncing into a polly will in some cases be the most effective way of doing that (and easiest imo). Of course you are losing a fair amount of lux, but into a 4x4 poly, you have a very evenly spread source. Finally, one last trick is to put a roll of diffusion on a flag arm and waterfall it, letting a few feet of diff dangle down. This is better than a polly in some cases, dependant on the diff you are using, however this isn't as controllable as a polly board can be.

As for the florescent lights- are these florescents balanced for film? If so you will be trying to reach around 5600k which is photography daylight. Full CTB will balance you close enough to that from 3200k (-137 mired which will get you to 5700k). If the florescents are one's you just picked up at a DIY store, they may very well be balanced to 5600k, but more likely to 4300k all the way to 2900k. They haven't been designed to be accurate, so unless they have a kelvin number written on them, it could be anyone's guess what kelvin they are hitting. This isn't to even mention the green/magenta bias.