Some options here – RST ones for 80 quid?

https://www.bike24.com/mtb-suspension-forks.html?menu=1000%2C2%2C121&sort=price_asc&__qf_form-filter=&pgc%5B87%5D%5B518%5D=1&pgc%5B100%5D%5B589%5D=1&pgc%5B72%5D%5B475%5D=1

Was going to suggest the RST Air…

https://www.bike24.com/p2188053.html?menu=1000,2,121
The RST’s have changable steerer tubes should you wish to reuse later.

or Manitou Markhour

https://www.bike24.com/p2251322.html?menu=1000,2,121

I’ve had a look at this too as a potential upgrade for a Whyte 604 with it horrid Suntour coil fork but another possible alternative is to replace the lower headset cup with something like (you’ll need to measure up / do your homework – understand whether you have a straight head tube or tapered) a Hope Type H ec44/40 which should open you up to world of tapered forks.

See p3 of https://www.hopetech.com/_repository/1/documents/HOPEHEADSETS2011Web.pdf to get a better understanding of the options.

you can get a straight tube pressed in if you can get a cheapish tapered fork

https://www.instagram.com/p/CEB9igBnTj6/

If you can find a Suntour Epixon in the U.K. they sometimes do straight steerer forks. They’ve got alloy stanchions and are fairly light / have some damping unlike the cheapie Suntour xcm / xct etc.