Don’t know if this will help assuage your fears: https://www.techradar.com/news/mullvads-no-log-policy-proven-after-police-raid
I’ve used Mullvad for years, and from what I know, they store almost nothing – only your randomly generated account number. If you are paying using an anonymous method that’s even less to go on.
Plus one for posteo. I’ve used them for several years now and have had no issues