I have my keyboard set to UK Extended. It's able to do most diacritics, so I just stick to it even when typing German and other suitable languages, like French.

I have my keyboard set to UK Extended. It's able to do most diacritics, so I just stick to it even when typing German and other suitable languages, like French. Umlauted vowels are done with AltGr+[ followed by the vowel. ß is done with AltGr+S. It's a tiny bit less ergonomic than having dedicated keys for these letters, but I consider the tradeoff worth it since the letters don't occur too frequently in German and I only need to memorize one keyboard layout. I don't know if something similar is available for US layouts.