I didn't see any (#)siteupdate post about it (maybe I missed it), but I noticed it was added (I really don't know how long it's been active). Now you can add a beanbag to your collection when you but it from a shop (user shop or NPC).

But THANK YOU staff, that helps a lot to my humble beanbag collection to grow while I quest.

Let's spread the love 'cause the "Add to Collection" buttons exist! ❤

This has been a thing for a while now, actually...and it's still one of the most awesome changes (along with it's predecessor, the add to wardrobe button) in recent memory. n_n You might not have noticed if they've been asking mostly for items you already have in your collection. Even a humble beanbag collection can still have most of the ones low enough in rarity for the quest givers to want.