2010 Vauxhall Combo ignition

When I put the key in the ignition and turned it, the ignition came on but the engine didn't start. The key in the actual barrel felt loose and like it didn't have the same connection it usually did.
When turning off & taking the the key out, the ignition stayed on. I tried again to put the key in and turn, but it didn't make a difference, ignition stayed on, key felt loose in the barrel.

I've tried the spare key for the van, no difference in feel and didn't turn the ignition on or off.

From what I can tell this sounds like I need a replacement ignition barrel, but after checking with some auto-locksmiths they're quoting hundreds and aren't too sure on the fix.
There are heaps of guides online for how to do this. I'm happy to give it a go but if there are is any solid/step-by-step advice out there I'd love to hear it before cracking open the barrel!