Two singles, as others have noted, solves this problem, and should not be more expensive (occasionally there are minor differences in taxes).

I think the flexibility on r/t awards has been improved recently as well, but it also used to be that booking two singles retained the full flexibility up until 24 hours on the return, whereas booking a r/t made the return 100% non-changeable 24 hours before the outbound.

I almost always book two singles rather than a return, but that's usually because I can't plan far enough ahead to decide both directions of any given journey at the same time!