I personally like Podverse.

I’ve never had issues with APKPure as far as safety goes. That and APKMirror are my main places to get apk files

You can definitely harden operating systems like Windows and Android to be better for privacy and security. I’ve used some of Techlore’s videos to make my Windows system a bit more secure and private, and he’s made one for Android and other OSes too. Of course, this isn’t perfect, but it’s something if you don’t want to install a different OS, it’s better than nothing.