Soldato
I'd start with which layout you want, which features (Hotswap, Bluetooth, VIA support etc..) and how much you want to spend.
If you're wanting ISO then I'd recommend Keychron (they have a UK site or there are UK vendors). You can buy an ISO, VIA supported hotswap board with keycaps/switches included and have a solid start to then tweak. Mod it with force break, buy a different plate, caps, switches and so on if you want to.
Monsgeek are also a solid option alongside others people have mentioned like Glorious etc..
OC sell the Glorious 65% and 96% boards along with Glorious switches and caps etc.. so you could get a full bundle plus some extras.
Honestly depends how far you want to go.
I'd say the main one would be hotswappable. Wireless support doesn't bother me so long as the cable detachable. I've just had another look at the Wooting site, which says the UK ISO 60HE+ version is in stock. The keyboard, wrist rest and a case can be bought for £220, which doesn't sound too bad consider the reputation it gets. Although not sure on what the limitations of the Wooting are in terms of changing things up like switches.