While I'm not going to disagree Switzerland is an OK option, you have to understand first why ProtonMail choose Switzerland.
One point being "In the US and EU, gag orders can be issued to prevent an individual from knowing they are being investigated or under surveillance. While these type of orders also exist in Switzerland, the prosecutors have an obligation to notify the target of surveillance, and the target has an opportunity to appeal in court. There are no such things as National Security Letters, and all surveillance requests must go through the courts. Furthermore, while Switzerland is party to international assistance treaties, such requests for information must hold up under Swiss law, which has much stricter privacy provisions."
I read this as, it isn't to say a government can't monitor what's going over the pipe for sigint, but if they specifically target a user for surveillance it must be disclosed to them and they have a right to appeal.
Nonetheless, if you're an American connecting to Switzerland for ProtonMail, the US govt will have some sigint, even if it's just your origin -> protonmail destination.
I'd go as far as to argue, as long as all communications are fully encrypted with the best possible encryption available (and no backdoors) it's fairly safe in any country for most general content. If you're extra concerned about privacy and surveillance (like I am), you should host in a country which has strong privacy laws but read up on the privacy laws, most of the time a country has good privacy laws for individuals, companies within the country, not foreigners.
Just my two cents away.