When it says direct debits coming out tomorrow, have a button saying keep money aside.
This way you stop your self buying a coffee and then the next day tour bills fails to go through and you get a bad credit rating.
Helps you have better control over your money.
Put the money in a pot and have all the direct debits take from that, problem solved
Most suggestions you could have a workaround easy enough. The point is to suggest something to make that even easier.
A button of “Pay now” actually isn’t a bad idea. Monzo deduct the funds and pay when the direct debit comes out. Kind of the opposite of getting paid early.
Have you looked into Bill Pots?
I like the budgeting aspect you’ve suggested here (which I think would work best if your bills come soon after you get paid), but I love the bill pots as I just pop the money aside as soon as I’m paid and can forget about it, knowing my bills will be paid on time. Especially as there’s one I can’t change the date of so it comes out just before payday which is really annoying 
No point reinventing the wheel, when a bills pot deals with exactly what’s needed. Especially when said suggestion would be a niche thing given there’s a work around which actually works.