You said "Backrest preferred", Before you buy a trunk with attached backrest, try the trunk alone. The C-14 doesn't have a lot of room and some people report the BR crowds the passenger. You can always order it later if there's room.
If you want a BR without the trunk, Pirates-Lair has one complete with rack. You'd need to move his rack forward to use with a trunk as it sits too far forward.
The Givi Monokey mount is probably the neatest one and they have a variety of sizes.
The newer OEM trunks are made by Givi and use the Monokey system. Beware though, earlier ones were Monolock and required a mounting plate.