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Pathfinder Monsters OGL and the paid "pro" version are slick. You might not need them often but when you need to find a Small CR3 Dragon or list of options for Monstrous Humanoid II it's pretty slick!
The grippli I see listed in Bestiary 2 has a 20' climb speed and is small. There's also a monkey goblin in the Inner Sea Bestiary if it's specifically the world guide that's a problem. There's a few more medium size I spotted too (morlock in Bestiary).
(This pathfinder monsters OGL app is pretty handy for stuff like this. Used it a bunch for the monstrous physique loving magus I built for a one-shot a while back.)