What alternatives do I have for insuring bitcoin and bitcoin cash payments (that I'll receive in the future) against falling prices? That's against the pound or euro. Obviously that's against an x% fee.
As of 2017, the CME and CBOE offer Bitcoin futures (but not bitcoin cash futures). AFAIK, these are the only regulated future contracts that you'll get. More ways of hedging your exposure to future bitcoin price collapses might be available in the future.
If you don't want to suffer the volatility of BTC and BCH you really only have one option: trade it for something less volitile. Namely, trade it for USD, EUR, GBP, or some other cash money.
You'd have to do this through an exchange. Collect your payments directly to your exchange account. I think some of them have auto-scripts that sell immediately at market price. This will give you near zero volatility, assuming your payments are always collected at current price.