My cheap Kogan mechanical keyboard arrived. It doesn’t feel as solid as the Akko (behind it in the picture), but it feels as nice to type on and it was only $17. The blue switches are a little noisy, but not horribly so. I’ll keep using it for a day or two, I think, before moving it to the family PC and going back to the Akko.
I bought a keyboard. It's an Akko 3087 v2 with Gateron Orange switches, and double-shot PBT keycaps. Thanks to @yojimbo and @Bitnacht I actually know what all that means now. Not quite the same as a BBC B keyboard (which had linear switches - I think BITNACHT's suggestion of Black switches might have been spot on), but it's a big step up from what I was using before. It was reasonably cheap ($89 AUD), and I liked the colour. The build quality is really good - it's solid and feels nice.