What a nice gift!! There are so many suggestions. I believe the one with the Koala clasp and rose interior is discontinued. So, if you are looking for a durable small agenda, in other words the PM size, consider a Damier Ebene one as it is very durable and will look nice against all the Mono you have. The Damier Azur is really awesome with Mono bags, but it's light so if you are concerned about stains, it's not the one for you. If you don't like the Damier patterns, there is the traditional Monogram. Or, consider the Mono Trunks and Bags agenda, it has a neat logo on it. Also, there is the Monogram Partenaire which has a snazzy clasp (but does not have the six rings).
The Multicolor in black or white is also nice, but it does have vachetta on the outside so it's a little more delicate. There are several leather varieties which require just a little upkeep: Suhali, Vernis, and Epi.
I love my Damier Medium Agenda (MM) as it is roomy, durable, worry-free, easy to write in, and fits in my medium-sized handbags. I have two small ones (Mono and Indigo Vernis) which I love but are too small for my everyday needs.
Good luck.