How should I buy or transfer Swiss francs from Singapore to Geneva?

Check out f.ex. CurrencyFair and Transferwise. Currency conversion by the banks is too expensive. You can open SGD account in CH, and send converted to yourself within CH by the mentioned services.

If you need to transfer SGD - CHF or vice versa, you can check out the remittance services like InstaReM or TransferWise. You can find out more here: https://seedly.sg/reviews/remittance

I used TransferWise personally, so should you decide to use TransferWise, here's a referral code to get a free transfer of up to $500: transferwise.com/u/waih47