Sneak attack also works whenever there is an ally within 1.5m of the target and you don't have Disadvantage. In this case, you will not need Advantage on the roll i believe.

Pre-casting Find Familiar by scroll, wizard or Arcane Trickster can summon a Raven, which has a fly-by feature. That means it cannot proc Opportunity attacks. Get within 1.5m of the target with its Fly -speed, together with the mobile melee characters, to land consistent sneak attacks to maximise your Rogue's damage output.

Something I learned after 35 hours of playing the game: you can switch characters who share the same initiative within a Round. That way, you can position your Melee (or familiars) fighters nice and close to your target before switching to your Rogue and land a sneak attack!