First off, there's 200 more practical things you can do first. A Faraday bag isn't going to accomplish more long term then your phone simply being stripped of bloat and tracking apps, or simply being turned off.

That being said, if you must, Mission Darkness bags are decent, and I've tested them and they do block WiFi, BT, and cellular signals.

YMMV, and understand that when you phone is in the bag, it might as well be turned off. You can't access it without opening the bag.