I went to collect my new glasses today and on the way stumbled onto one of those random neighbourhood fleamarkets that you find in summer in Stockholm. On the first blanket I passed was this, for $3. It is used, and needs a quick clean, but other than that it is in perfect shape, and great for travelling as it is so small and the interior layout is nicely designed.
I don’t have a slimline anymore, because I prefer binders with straps, but these ones fit much more easily into pockets and flaps on travel bags than the bigger ones do. A previous Slimline that I loved to bits and used a lot while travelling was my Filofax Classic Slimline in black.