Hey 
I’ve started uploading the Monzo APK to apkmirror.com … They’re the biggest most trusted distributor of APKs but ofc, it’s entirely your choice 
https://community.monzo.com/t/monzo-for-android-beta-channel-changelog/10207/528?u=nexusmaniac
I run on the beta channel so most of the uploads on apkmirror will be beta releases but monzo is incredibly stable regardless.
Hope this helps!