Your baseline camera is the SL2S, which means you have a certain expectation of image quality. The numerous suggestions can be ranked as follows:
high image quality:
Leica Q family
Sony RX1 family
medium high image quality:
Fuji X100 series
Ricoh GR aps-c cameras
decent image quality:
micro four thirds cameras including GM1, GM5, GX880, Olympus EP-L series,
mid-decent image quality:
1" sensor cameras like the
Sony RX100 family
Panasonic LX10
Sony RX0
Canon G5x / G7x families
Lower image quality:
small sensor cams including Ricoh GR D family, Canon Ixus/SD family, etc
If you want something small and fairly pocketable, the Sony RX100, Panasonic LX10 and Canon G5x/G7x are excellent options.
Having owned many small sensor cameras like the Ricoh GRD III, Canon S90, Fuji F30 etc, I wouldn't recommend them to someone who owns a SL2S. They just don't have the dynamic range and colour depth of a 1" sensor cam like the Panasonic LX10 or Sony RX100 V.
Panasonic LX10
LX10 - The Little One by
Archiver, on Flickr
The closest is the Panasonic LX7, which is an awesome small sensor camera that somehow has the same or even better dynamic range of the Canon 30D in raw! In fact, I might buy another LX10 to replace my old, faulty one. I like it that much.
Panasonic LX7
LX7 - In the shadows of the arch by
Archiver, on Flickr
A lot of people like the Fuji X100 series, but I can't get past the smudged green foliage that the later X-Trans models produce when using Lightroom. If you like X-Trans, that's fine.
A micro four thirds camera isn't pocketable, no matter how small. But the image quality from the 16mp models and up is excellent, especially when paired with primes like the Olympus 17/1.8, 25/1.8 and 45/1.8.
GM1 with Olympus 25/1.8
GM1 - Lumix by Lumix by
Archiver, on Flickr