I would love to have the option to top-up my account on the first day of every month to an certain preset amount.
For example, to top-up my monthly spending account to €1000,- every 1st day of the mount. When I spent only €800,-, it will top-up with €800,-. If I spent the full €1000,-, it will top-up €1000,-.
This way I have only €1000,- to spend every month regardless of my spendings the months before.