Doubt you'll find a 4ml spiral in the UK, Fastech have the 4ml one, if you use UK express postage, you should have it in a week.
It's got good flavour on stock coils, rba is a step up again on flavour, I don't use Smok coils(out of 15, only 3 didn't burn out so I only use the rba), 24ga kanthal 25mm 5 wrap works out usually about 0.7ohm.
Tried Clapton's, twisted too but for me normal kanthal wire is best on the Spiral.
It's very very fidgety/frustrating at first as the decks tiny, but once you master it, it's very easy to build and wick from then on in.
Don't ram masses of cotton in the wick hole, it'll dump the juice out the air holes, less is best with the Spiral.