First off, the answer to your question is something EVERYONE would like to know. There are fund managers at Fidelity who will a pay $100 million fee to someone who can tell them a "safe" way to earn interest.
The first thing to decide, is do you want to save money, or invest money. If you just want to save your money, you can keep it in cash, certificates of deposit or gold. Each has its advantages and disadvantages. For example, gold tends to hold its value over time and will always have value. Even if Russia invades Switzerland and the Swiss Franc becomes worthless, your gold will still be useful and spendable. As Alan Greenspan famously wrote long ago, "Gold is always accepted."
If you want to invest money and make it grow, yet still have the money "fluent" which I assume means liquid, your main option is a major equity, since those can be readily bought and sold. I know in your question you are reluctant to put your money at the "mercy" of one stock, but the criteria you have listed match up with an equity investment, so if you want to meet your goals, you are going to have to come to terms with your fears and buy a stock.
Find a good blue chip stock that is in an industry with positive prospects. Stay away from stuff that is sexy or hyped. Focus on just one stock--that way you can research it to death. The better you understand what you are buying, the greater the chance of success. Zurich Financial Services is a very solid company right now in a nice, boring, highly profitable business. Might fit your needs perfectly. They were founded in 1872, one of the safest equities you will find. Nestle is another option. Roche is another. If you want something a little more risky consider Georg Fischer.
Anyway, what I can tell you, is that your goals match up with a blue chip equity as the logical type of investment.
Note on Diversification
Many financial advisors will advise you to "diversify", for example, by investing in many stocks instead of just one, or even by buying funds that are invested in hundreds of stocks, or indexes that are invested in the whole market. I disagree with this philosophy.
Would you go into a casino and divide your money, putting a small portion on each game? No, it is a bad idea because most of the games have poor returns. Yet, that is exactly what you do when you diversify. It is a false sense of safety. The proper thing to do is exactly what you would do if forced to bet in casino: find the game with the best return, get as good as you can at that game, and play just that one game. That is the proper and smart thing to do.