Hello 
I looked everywhere but I’m not able to understand if in switzerland the status of registered partnership is only for the same sex couples or not.
If not : have I to declare a partnership or can I live as a single individual with my partner to Pay less taxes ?
The registered partnership (eingetragene Partnerschaft) is the marriage equivalent only open for people who can’t marry (same sex etc.).
What is your reason for thinking about registering? Inheritance, partner rights…?
Yeah, just live as a couple without marriage and save taxes. 
No just to be in the safe side because in a lot of declaration about my legal status I always see this option.
Background:
In Italy when you are going to register you and your partner in the a new city you have to declare to be a couple ( also if you are not married ).
Thanks for clarification 
My understanding after the vote on marriage for all was that creating new registered partnerships after July 1 is no longer possible, as marriage is now the way to go for everybody.