@BlankHotel It's difficult to give you advice without a budget or any idea of what you want out of the computer. The options available at £500 are dramatically different from those available at £700, while over £1,100 or so (depending on current sales), you wouldn't necessarily get any benefit out of further upgrades, at least where Sims 4 is concerned.
And that's just for Windows PCs. Macs are simpler to summarize, and also more expensive for the same performance. If you already know you'd prefer a Mac, that's one thing, but if you're indifferent, a Windows PC would be the better option from a performance standpoint.
I can offer two different kinds of advice here. If you're not ready to buy yet, I can list the kind of hardware you'd want to look for. If you are ready to buy, as in now, I can look for the best options currently available. In either case, I do need to know at least an approximate budget as well as whether you want a Windows PC or a Mac and a laptop or desktop.