Upgrade XS Marlin fork

Pre-teen dirtbag (11) is starting to hit the downhills a bit harder on his hand me down 2022 XS Marlin 27.5. I’ve put DHF/DHR tyres on it, wondering about upgrading the stock Suntour XCT fork which is definitely going to start holding him back. Obviously don’t want to spend more than the bike’s worth, especially as he’ll only be on it a couple of years. So ££ is a constraint. Other constraints: QR axle I don’t really want to change if I can avoid it, and straight headset. Already down with the idea I might need to buy a tapered headset adapter as apart from the Judy it’s really hard to find any straight steerer forks these days. Don’t mind going second hand, even early/mid 2000s if necessary. Any recommendations of things I could consider?