Help with buying a new gaming pc to play all The Sims 4 and Packs

@Simsfan8989  If you're going to get an Alienware, start with this configuration instead:

https://www.dell.com/en-uk/shop/gaming-and-games/alienware-aurora/spd/alienware-aurora-r8-desktop/d00awr801?view=configurations

It's almost the same hardware for £729, and you can get a couple more upgrades while still staying under budget.  This is what I'd suggest, in order of most to least important:

• A 512 GB SSD (+£70), or
• A combination 256 GB SSD/1 TB HDD (£50) if you need a lot of storage
• An i5-9400 processor (+£80)
• An Nvidia 1660 (+£60) only if you plan on playing other more demanding games at some point
• Not the extra memory.  You could get a matching RAM stick for maybe £40 and install it yourself, rather than paying Dell £100 to do it for you.  Installing memory is just about the easiest thing there is to do with a computer: you open the case, push the module into the slot, and you're done.

Your old monitor should work fine, as long as it's not extremely old.  You can check which connector it uses, and any other ports it has, just to make sure, but if it uses DisplayPort or HDMI, it will plug into any new graphics card.  If you're not sure what the monitor uses, you can find pictures of various kinds of connectors and compare them to what you see.

Sims 4 runs the same internally on old and new monitors; the only detail that matters is the resolution at which the graphics card is displaying the game.  A higher resolution means more work.  If your old monitor is 1920x1080 or below, an Nvidia 1650 will be able to run the entire game on ultra graphics settings with plenty of room to spare.  The only difference is how the game looks on the monitor, so if you don't feel like you need a new one, there's no point in buying one.

Edit:  The one on Curry's website is significantly better.