I agree that breaking it down to a daily budget that is a combination of essentials and discretionary spending is probably unhelpful, especially as you say you want to meal plan more, which probably means buying in food for a few days or longer so the ups and downs in spending day to day will be large.
Some days you will eat cheaper food and others it might be more expensive. If you make a roast and use the leftovers the next day, which day's budget does that food come out of? Is a takeaway, that is usually far more expensive than home cooked food coming out of the 'meals' budget or the 'treats' budget? Do you shop day to day, week to week, or do you shop for the store cupboard, and buy in bulk when you get paid, or see a special offer?
You probably need to go through what you're spending right now and look to see where you can cut costs. The MSE budget planner linked to above will signpost you to reducing the cost of things like gas, electric, broadband, pay TV, mobile phones, insurance etc. If you always pay full price for these things and have never shopped around, you can probably make a good saving.
With food, think about not wasting any, shopping at Lidl or Aldi if you can, or if you choose one of the more expensive supermarkets, buying as much as you can on offer - stock up on non perishables so you never pay full price for things that are always on offer, or try own brands.
Also think about what a meal costs to make and include some cheaper meals in your repertoire if you need to cut down. Small changes can massively reduce what you spend on groceries, eg frozen fish instead of fresh, normal broccoli instead of tenderstem, Asian branded spices instead of Schwartz jars, bigger packs of toilet roll, instead of buying a 4 pack each week, only buying cleaning products and toiletries when on offer, you get the idea.
If you manage to cut your costs, you should naturally build up savings funds, which can be used for annual and irregular expenses (car MOT, Christmas, insurance) plus less frequent costs like car repairs, washing machine repairs.