Learning to juggle way back lasts century, I learned to juggle using lacrosse balls. Very bouncy and and a little on the heavy side. Standing over a bed helps if you are using bouncy things (they still can cause havoc in a bedroom when they bounce off each other though).

One of the IJA (International Jugglers' Association) videos that most impressed me is : IJA Tricks of the Month by Zaila Avant-garde | Juggling Basketballs (https://www.youtube.com/watch?v=sH2E1m8Fseg). Not only does she manage the juggling but her parents let her do it indoors with all sorts of stuff around.

If you do use tennis balls, stand in front of your couch so they land there and don't roll away.

This. Something like a hacky sack also works very well. They don’t roll away from you, and they won’t drive your neighbors nuts especially if someone lives below you when they hit the ground.

Part of the motivation is to make sure you catch them and they don’t bounce away. Negative externalities aren’t always a bad thing.