Monitor for Macbook

It appears budget will be your main driving force, next is to consider resolution (1080p or 4K). You will struggle to get a 4k screen for under £200, there are many sub £200 options for 1080p monitors. Next is the interface - you can either buy a monitor with the relevant port or purchase a dock to enable more traditional interfaces. Do you need calibration?

The only thing you definitely need is connection compatibility, and the details of what will depend on which macbook air model you have.

There's not much else that's essential. You probably want to make sure the ergonomics work for you (appropriate height stand, accessible button placement etc.)

The biggest thing that's cause a suboptimal picture would be buying a monitor with a resolution beyond your laptop's ability to handle but that's generally the more expensive end of the market so not much to be concerned about if you're on a budget.

I have a couple dell monitors. I got them at the start of the lockdowns. I think I paid around £250 each new from Dell. Which at the time I was very happy with. I need more monitors now. So I checked eBay and they are going for £100. They are really good and I recommend them. It's the DELL ULTRASHARP U2518D