Good day
In principle, there are four possibilities:
1. you and your girlfriend each open a bank account. However, this is not a real joint account.
2. you or your girlfriend open a single bank account and give the other person power of attorney over the account. This is also not a real joint account. Possible advantage: Uncomplicated. Disadvantage: In case of dispute, one person can simply "kick out" the other.
3. the real joint account or "Compte Joint": the account is in the name of both persons. You both have individual signing rights. So you both can independently access and decide on the account balance without the consent of the other person. (Possible disadvantage: In case of death, the heirs of the other person can then have a say, but you can prevent this with an exclusion clause).
4. a collective account. Both persons have a collective right to sign. Both persons can only dispose of the account with the consent of the other person.
Which solution is best for you also depends on your individual situation.
Compare accounts
The actual joint account is offered by many larger Swiss banks and usually does not differ in terms of fees from a normal private account.
For this purpose, it is best to use the private account comparison on moneyland.ch with debit card. (In your case, there is usually an annual fee for an additional debit card).
Note: For adult personal accounts, the "mobile bank" Neon is often the cheapest at the moment, but you can't set up a joint account there yet.
Best regards from Moneyguru
More info:
Account comparison including debit card