The Rollei 35S has the Sonnar lens, while the 35T has the Tessar. The Sonnar is great, but when shooting wide open, you don't have much room for error when guessing focus. I've probably shot 100+ rolls with one of the Rollie 35 cameras. They're very solid, but you want to thoroughly inspect the camera.
Make sure that the film advance is working correctly. After moving production to Singapore, a key metal gear in the film advance was replaced with a nylon gear. It worked fine, until a heavy-handed user reached the end of the roll and forced the advance, which sometimes broke one or more teeth from the gear, rendering the camera useless from that point on.
Rollei eventually returned to using a metal gear.
Also, check that the lens collapses properly. The film must be advanced and the shutter tensioned before the lens can be collapsed. Again, some users forced the lens to collapse without winding the film, permanently damaging the mechanism.
The SE and TE models use LEDs in the viewfinder (and I believe a selenium cell, rather than a cadmium disulfide cell). While more accurate, they require a 5.6-volt battery that isn't easy to find today. And I find that metering in the viewfinder is very clunky.
The original design of having a waist-level match-needle meter system is superior for this camera. You can see the aperture, shutter speed and meter needle all at once.
It also seems that many, many Rolleis have a ding in one or more corners. If you can find one that doesn't, consider it a bonus.
To get to a really pocketable camera, you'll want to move to the modern day cameras.
There are a number of Japanese rangefinders that might fit the bill, including those from Olympus, Canon and Konica. They all will need to have new light seals installed. No exceptions.
German cameras rarely have foam light seals, as they used a better design for the back that didn't require foam.
I concur with the thoughts about the Cosina Voigtlander -- they are excellent value for the money.
Some of the early Kodak Retinas are pocketable, but will need to be serviced before they can be used.
Agfa made some very nice lightweight 35mm cameras, starting with its Solinette II and Super Solinette and continuing with a number of other cameras. The knock against nearly all of Agfa's folding cameras is that the lens is often frozen from lubricant that has hardened to near concrete and plastic-covered bellows that easily develop pinholes.
Also, Voigtlander's folding Vitos and some of the rigid-front Vitos are excellent cameras. Get one with a Skopar.
Zeiss Ikon had the folding Ikonta/Contina, Contina II and Contessa and later its rigid-front Contessa, which is an excellent camera.
Agfa toyed with half-frames, and its Optima-Parat is excellent.
If you have the money, a prewar Zeiss Ikon Tenax II (shoots square photos) is outstanding, and the uncommon (not rare) postwar Tenax with a Tessar is another good choice.
An oddball choice is the East German Werra -- great lenses in a small package and very well made. It came from Carl Zeiss Jena -- one of the few cameras ever made by a Carl Zeiss company.
I forgot the Ducati. But it's a niche camera that you probably could call rare. Plus, you need the tiny special film cartridge.
You can read more about these and many others on my site.