I use an app called Daily Budget that I find really useful. The idea is you enter your recurring payments, your salary and how much you would like to save each month, the app then calculates how much you can spend per day. Anything you don’t spend gets spread over the remaining days and if you overspend, your budget is reduced. I personally find it hard to gauge how much I can spend using the existing monthly view.
Monzo does a lot of this already, it would just be nice to have it all integrated in a single app.