Proton Mail is good (just not as good), but you can't integrate external SMTP for outbound emails; you have to pay to send from @yourdomain.com.

With Gmail, you can configure an external SMTP server using "Send mail as" setting. Super convenient. Tons of mail services offer a generous free tier for personal use (e.g., Mailgun 100 emails/day).

It's not really worth paying just to send a few personal emails from @yourdomain.com each month.