I recommend and use Mullvad as well. Paying with non KYC coin from a private wallet using a private server set up with good opsec is the way to go.

But again, it depends on your threat model and usecase. If you are using your identity associated paid Proton account, using the Proton VPN included with your subscription is fine. It's great for giving you privacy from your ISP, circumventing geographical limitations, and even torrenting, optiinally using another provider's VPN like Mullvad or IVPN or a Proton VPN plan not associated with your identity.

"Support for paying with Bitcoin when you first sign up is coming soon. Until then, you can sign up for a Free plan and then upgrade using Bitcoin"

Where you need more privacy, sign up and use a free nym Proton email account (not associated with your identity) optionally using another VPN provider like IVPN or Mullvad or a Proton VPN plan not associated with your identity.

Where you need as close to anonynity as possible,  sign up and use a free nym Proton email account (not associated with your identity) over Tor only.