Any of these would work, but I don't know the layout of the laptop, so there's a few different shapes and sizes here:
EDIT, direct links removed.
Try looking for these on ebay, the results are basically all for the same thing -
Internal Network Antenna MHF 4 Dual Band WiFi Wireless or
M.2 Internal Network Antenna MHF 4 Dual Band
obviously ignore all the results for the screw in external antennas, but anything with the tiny Ufl connector will work, the antenna shape on the other end might be square or long and thin, but whatever you can fit in the laptop would be fine.
They're relatively generic, so most of the sellers seem to have variants of these ones. I can't find any UK sellers, so it might take a couple of weeks to arrive. All the ones I can find are all sold in pairs, I think for MIMO modules, but the antennas themselves are identical. I'm not 100% on whether the new module uses 1 or 2 antennas, but it think it is just 1.
I'd try with just the old antenna first, and see if you get 5GHz as well, then if not, try connecting a single one of the dual band antennas above, and if it all works, then you can route the antenna away in the case somewhere. If it does have two antenna slots, just add the other antenna later, after you've got it working. It would still pick up signals with a single one, the other is just for increasing throughput.