Our take-home income is just over £4k per month.
We spend quite a lot on food (I like to buy organic where possible) and health (apps, supplements and so on) but other than that we live modestly. We eat very little meat.
We own our house outright. Council tax is about £2.5k a year. We have two, one-week, UK-based holidays per year, usually not during the school holiday times. We haven't been abroad since before Covid and haven't been on a long-haul holiday for over a decade. Most of my clothes purchases nowadays are 2nd hand, usually from Vinted, or in the sales.
We run two cars, both of which we bought used and are over 10 years old.
We mostly live within our means, only occasionally dipping into savings to pay for large or unexpected expenses. Any surplus money we have at the end of the year goes to the grandchildren's ISAs, usually about £4k per year.
I think we wouldn't be able to live life as we want to on £2.5k per month. We would inevitably be cutting back on something or dipping into the savings more.
I think the best thing to do is look at all of your spending for the past 2 years, take out commuting costs and other costs that you won't incur when retired. Then divide the total by 24 to get an approximation of your liking monthly spending.