Skiff or Protonmail.
Skiff gives you 10 GBs of storage and also comes with a drive and a Notion-like Pages app. They even let you add custom domain for free. The only disadvantages are the non-native Android or iOS apps that just feel off and the limits on folders and filters.
ProtonMail only gives 1GB of storage and stuff like custom domains, aliases, etc are all paid features. The Android app is decent but missing some basic features that you only notice when you actually use it (select and delete when searching for example). Definitely the most robust mail service there is though. With Proton Unlimited, you also get stuff like per-site aliases using SimpleLogin, Proton VPN, Proton Drive, Proton Calendar and Proton Pass. But if I'm being honest, only the Mail and VPN are truly complete products.
I kinda get you, but I'm (not oc) using forwarding as a temporary solution until I've slowly moved everything away from Gmail entirely. It's also good to import all past mails over.