Self-custody is an impossible ideal, because there won't be enough utxos for everyone, and even if there were, my mum would never be able to take advantage of it.

Fedimint is a good solution to this problem, but it's even more than that. It seems that the fact that it doesn't involve a Blockchain creates new interesting uses-cases, for exemple, I've seen people developing modules for it and this looks very promising, and exciting!