bigger bikes for little people

My sons hardtail will soon be ready to go to pastures new, and I'll be on the hunt for a 140 or 150mm travel full susser. He isn't that big so I'm looking for a 27.5 XS or maybe a small womans bike with a price around £2200, maybe I can squeeze a little more if I sell a few bikes that are lying around here not doing much.

What's good for little people sub 5ft, I'm thinking a Stumpjumper S1, transition Spire looks good but too expensive.. I know this bike will be outgrown so expect to be selling it in a few years. Looking at the current secondhand market, people are expecting covid prices and with new bike prices tanking, I'd rather put my money into new as opposed to old.