There is no “official” way to download Android apps. F-Droid hosts a lot of great open source apps, for the rest of the Android world, there is Aurora Store which downloads directly from Google Play.
What do you mean with “it crashes with 30% of the apps”? What happens? Can you just not install them or do they not work after installation. For banking apps, it can be hit or miss on SailfishOS. You can download them from Aurora Store and check here if they will work/not work/require some extra steps to work.