@elinormaryy You can certainly get a laptop capable of running Sims 4 on ultra graphics settings, including all current packs, for less than £800. All of the laptops I'm linking will do so. The question is whether you want to spend a bit more for faster hardware, for example if you want to play at higher refresh rates, or with a lot of high poly (high-resolution) custom content, or add Reshade or a similar utility to the mix. A faster graphics card wouldn't be strictly necessary even then but would help keep the game running more smoothly with the extra demands you'd be placing on it.
This laptop is the cheapest good option I'm seeing: good enough for ultra settings, 16 GB RAM (nice to have but not required), good build quality overall.
https://www.argos.co.uk/product/3268753?clickPR=plp:2:49
These have a graphics card that's one tier faster:
https://www.currys.co.uk/products/asus-tuf-gaming-a15-15.6-gaming-laptop-amd-ryzen-7-rtx-3060-512-gb-ssd-10259874.html
https://www.overclockers.co.uk/asus-tuf-gaming-a15-nvidia-rtx-4050-16gb-15.6-fhd-144hz-amd-r5-7535hs-gamin-lap-asu-01713.html
If you want an upgrade and a bright pretty screen, this is worth considering, although Sims 4 will never use all that power:
https://www.argos.co.uk/product/6824802?clickPR=plp:19:49
These are just a sample of the many options in your price range. So if you don't like them for one reason or another, let me know why, and I'll narrow the search accordingly. And if you have more questions in general, please feel free to ask.