There's no English keyboard.
Writing French with the US international layout is actually pretty easy.
The umlaut is a dead key so it's very easy. ß is AltGr or Option + S which I admit is a bit more annoying, but your spellchecker should take care of that, no? (I'm Swiss so even when I have to type in broken German, we don't use the ß here).
All layouts are tradeoffs. Not using the US layout makes a lot of things annoying in our field. I write code and use my IDE's keyboard shortcuts more than I need to write long texts in my native language.
I've switched to US intl 15 years ago and I don't type in French any slower than I used to. On the other hand I benefit greatly from using the default layout in our very US-centric field.
So " is Shift+' and @ is shift+2
In UK keyboard layout, @ is shift+', and " is shift+2 (which is what is shown on my keyboard keys).