I've been running almost like for like in the playerroles as you and had decent success doing so, however, i have way more indepth TI's.
First of all, Douglas Costa is absolutely not what you're looking for in a Mezalla in this formation. You need someone with good workrate, decent tackling and even if it's not highlighted, positioning. In fact, you have pretty good options for that role in Ramsey, Bentancur and Can. Who of these will do the best job for you depends on your overall team instructions imo, but speaking from experience the Mez-s in this system plays mostly like a box to box.