Q's solution is the most easy and is considered acceptable (it comes originally from using keyboards without the extra letters). The new 'ss' rule is: 'ss' after a short vowel and a diphtong and always in Switserland, ß else. So it is now Kuss (kiss) and Fuß (foot).

For Mudgard's solution:

type ä to get ä
type ö to get ö
type ü to get ü
type ß to get ß

Wolfgang