You can consider a title "Business Process Manager", unless you feel that the position is really a C-level position, then COO is exactly that.
Have in mind that all positions should be taking pressure off you, and that doesn't make them high-ranked positions.
It also matter of company size (# employees) and structure. If its a big operation, and you don't have a COO, you might as well go with that.
As you will be headhunting for a similar profile in both cases, I would advise you put both on the job ad: Business Process Manager/COO, and decide according to candidates.