Hi Pamela, It all depends on personal preference; rolled oats (old-fashioned) would be the most common to use, but you can also use quick oats, although these might be a bit fragile and not give you the texture you are looking for. You could also try thick-cut rolled oats such as Bob's Red Mill Oats as a possible other alternative, which may give you more of a crunchier texture.
You could also add a touch of chocolate to them if you want to make them a little more luxurious.
The cookies will be best on the day they are made but will last up to a week in a sealed container with parchment. Ensure you keep them away from moisture. If you add chocolate to them, they will last up to 3 days.