I would keep the base currency in EUR if that is your reference currency.
This only impacts reporting for returns.
The question that remains to be asked is what you do with your cash, especially if there are large amounts.
For small amounts, I would leave the cash depending on the amount you received from any dividends or proceeds from the sale of securities. This avoids unnecessary transactions.
For larger amounts, especially if you plan to keep the cash for a long time, it's worth exchanging it into your main currency. You can also invest a portion in Swiss francs to take advantage of their strength.