A Denon remote will be best because the buttons will be labeled with the exact function names, while universals will either have poorly labeled hard buttons or (in my opinion) cumbersome soft labels.

That said, a Harmony will have Denon codes, and if any functions are missing, you can usually get Logitech to add them. Professional help is not necessary.

A very cheap solution is to get nearly any OneForAll remote made in the last 5 years or so (new for less than 20 pounds, and of course less used ). These remotes have Denon codes built in, and additional functions can be added manually. For example, the function System Setup will in most cases be programmed to the Guide button, but if it isn't you can add it by entering 33855 using the "Key Magic" capability of the remotes.