if you wanna have it even easier, you may do it like that:
but just when your writing with PC, never when youre writing with hand...
people in midage wrote like that then.
And concerning your question: Im German and sorry, but I dont feel automatically offended if someone´s using it.
I agree with the fact that its old-fashioned and normally not used. But if its used it depends strongly on the context how to interpret. There are of course phrases like "Frollein, so nicht!..."- kind of a ban.
But it might be jokingly as well. And if I have a chef (if he´s older and we do have a good relationship) who´d address me like that - Im not sure if I would feel sooo strange. With older people in general not. True, its not modern any more.
I´d really advise you to buy a modern excercise book, as
1. Language (mainly words of course) and language use change rapidly and steadily(!!!) more than 40 years (the book´s age) is a lot!
2. Teaching methods and knowledge about it have changed,too. Books and excercises from that days look much different from the ones nowadays - and there are really good ones. New facts about learning have been discovered and everythings been developed.
Id even go a step further: At that time language skills and language accuracy and precision might have been not that appreciated as nowadays.
3. The last fact: There have been various spelling reforms in the last years
So, please- buy a contemporary excercise book