you could also set up a compose key with a custom key combination for @. (like Alt+a,o or something)
I think you just have to install Gnome Tweaks and set it up there (in Budgie anyway). not sure about setting custom combinations exactly because I haven't done that yet.
but basically it's much, much easier than memorising alt codes. Compose+1,2 gives you ½
. Compose+s,s gives you ß
. it's really handy!