For handles on rose...
If you have chosen a handle on rose, you may want matching keyhole escutcheons if you want to be able to lock the door. An escutcheon is a piece of door furniture that hides the cut out keyhole in the door. It matches the door handle, and finishes off the door.
For the bathroom, you will probably want a matching thumbturn and release. The thumbturn part fits on the inside of the door so that it can be turned for privacy, and the release part fits on the outside of the door for emergency opening. Since this is used where privacy is required, it could also be used on bedroom doors.
The kit is not yet complete... you have the looks, now its time for the mechanics. If you are using the lever alone, then you will need a tubular latch to make it work.
If you are using escutcheons or thumbturn/releases, you will need the correct locks to make them work. Handles used with escutcheons will require 3 lever sashlocks, and handles with thumbturn/releases will need bathroom locks. If you are fitting the handles into new doors then you will need to buy these along with the handles. If you are replacing existing handles, you can use existing locks, but make sure:
For handles on plate...
For a handle on a plate without a keyhole, all you need to make it work is a tubular latch.
For a handle on plate with a keyhole, you need a 3 lever sashlock.
For a handle on a plate with a thumbturn and release, you need a bathroom lock.
As for handles on rose, if you are fitting new doors you'll have to buy these locks/latches when you buy your handles. If you are replacing existing handles you can use existing locks providing: