IMO- unless you object to a coaster brake, I'd simply use your existing TCW as is. The issues about brake failure are overblown, and in any case you have the front brake already.

For the record, and to give you a sense of proportion, SA made and sold countless numbers of this hub over a span of decades. The problem, such as it is that if the gear cable is trimmed wrong and allows the hub to drop into the "dead zone" between 2nd 3rd, you'll lose the brake too. It's manageable by keeping the hub adjusted, and after all, you don't want to drop into the dead zone when pedaling either. Both the ubiquitous AW and TCW share this flaw(?), and many of use wouldn't be here today if it was as serious as people would have you believe.

But realistically, rear brakes are really only speed check and control brakes, and hard stopping power can only come from the front brake anyway.