I second this. If you keep it in a container or a jail or something, you can run it on a server you control, set sshd to do password authentication, have one really good passphrase, and now you can access it anywhere you can get to a shell with ssh and Internet access. (This is obviously less secure, but the convenience is great if you need it.)

I've also done a version of this where it's stored on a Pi Zero, but the Zero (and SD cards) isn't the most reliable thing in the world and lost it a couple of times before I gave up, but it may work for others better.

It's more fiddly than a more featureful service, but I like it because I understand all of it and control all of it.

Second this too!