I use EurKey [0] (I think this was actually recommended to me on HN) so I have easy "AltGr" access to German characters like öüß. Sadly some tools (most notably Microsoft’s) have hardcoded shortcuts for some of those, which is really annoying.
I use the Canadian English layout on macOS for most of the time, if I need to enter accented letters, I can just hold down a normal letter (A) then select an accented one from the popup (Å). The international English layout works the same way if I remember correctly.
[0]: https://eurkey.steffen.bruentjen.eu/