You did not describe the design or detail of your collar. Any weighted features - tight fitting may cause discomfort.
Weighted features - places to hook up leashes chains etc.
Tight fitting - should be able to at least place 2 fingers comfortably between the collar and neck.
Thickness and height also plays a part in this - think petite or heavy duty butch dog collar.
Bare unseasoned leather would be sort of kind of rough on tender neck skin. After a period of wear the roughness may weather
to a more smooth application - Great idea to line the collar with some soft material - but beware prolong wear may expose the
rough edges of unseasoned leather and any cosmetic make up may present other problems staining retaining moisture etc.
Upon receipt come back and tell us more - Oh and is this a lockable collar (my specialty ! )