I was considering switching over to Tuta, but haven't spent the time on it yet. Did you end up moving to another provider or hosting your own?
Just put your domain name for registration. It will say it is registered already but then offers you the option to buy email hosting. I think it is 18 Euros for 5 Email accounts per year. It is based in Switzerland.
Australian fastmail may be better - I don't have experience myself - but it starts at 60 dollars a year. Maybe someone who is a user can give feedback here.
Regarding infomaniak: They offer a free email service (without your own domain). Maybe you try it out to get a feel if this is right for you and your domain: https://www.infomaniak.com/en/free-email
And hands off to apps that have a registration code. E.g. pleco. They are not linked to your email and you don't lose them if your gmail is gone...