Is it though? The OP talks about there always being something unforeseen that crops up, which suggests that her budget isn't as comprehensive as it needs to be, because there shouldn't be much that is 'unforeseen'. Perhaps the OP can give examples?
But these sorts of threads are pointless, because even if a 'comfortable disposable income' was agreed, what is the OP going to do? She might not have any practical way of increasing their disposable income that doesn't have an unpalatable detriment to her lifestyle. Plus everyone defines disposable income, essentials and savings differently, so it's another 'how long is a piece of string' question.
But for the OP, you need to make the best of your circumstances. It sounds like you have a decent income so you have to make it work for you according to your priorities and be mindful that every pound you spend on A is a pound less that is available to spend on B, C, D etc.
Can you reduce the cost of your bills/groceries? If you're one of those Mumsnetters who think artisan sourdough, large servings of protein and unlimited blueberries are basic essential groceries, you need to accept that a good portion of your 'nice things' budget is being spent there.
How much does the household spend on food and drink out of the house? That could easily be hundreds of pounds a month, so needs to be done mindfully, to make sure it's worth it to you, and see what can be swapped to cheaper alternatives, eg nice frozen pizza instead of delivery at 2/3/4 times the cost.
Have you reviewed all your bills to get them as cheap as possible. You should always be on a deal for everything.
Days out don't need to be expensive. If there's places you like to go regularly, get a membership, rotate around so you have one or two at a time, then cancel and swap to something else. Take a picnic instead of buying food out, which is usually poor quality, expensive and at the end of a long queue.
When you consider most people, ie excluding those who don't have enough to pay all their essentials and the people who can spend endlessly without running out of money, the likely biggest factor in how 'comfortable' they feel is how they manage their money and spending, not how much they have. Some people will feel very comfortable on £500 pm and make it go quite a long way, whereas others will rinse through £5000 pm and not feel particularly well off.