We use Tile trackers. I have an android phone and my partner has an iPhone. The trackers seem to work well and are reliable. The app we use them with is Life 360. Just the basic version, not the paid subscription.
Came in quite handy when my check in bag was lost in the way back from Japan. I knew pretty much where it was all the time and could track it as it was being returned to me.
We have had a few issues with the app crashing but we just log out and back in again and all is well. HTH.