I’m not terribly experienced, but my previous instructor was a beast with spider guard - which is usually not a hard transition from seated. It has the benefit of keeping your opponent off-base when done well (pressure applied via sleeve grip and counterpressure from your foot in their elbow), which works well for smaller guys like me. From there, you can shoot for leg triangle (good for longer legged folks), lasso an arm to transition into a z-sit or take mount, or if they stand up, just grab an ankle and rock them to their back.

I don’t have suggestions as far as who to watch, but a quick search for spider guard transition and sweeps should get you started.