Crown is 24mm
http://www.uwell.cc/showpro.asp?id=8
TFv4 does come in a Mini (finally in black as well as stainless). Though a few things, first IMO TFv4 is the best option IF you're interested in rebuilding your own coils, if not you may be better off with alternate options as the coils are expensive and really suck up the juice, so it's going to make more of a dent on your wallet than something like the Herekles or Crown. Also, the mini heats up fast, so using higher wattages could be a bad idea, for me 80w it was starting to get hot after a few hits, at 50w though it wasn't a concern at all. I'm a big fan of the TFV4, but it has it's pros and cons like everything.
I know for a non rebuildable option the Herekles Plus that's coming soon looks pretty fantastic, sharing coils with the Atlantis (and many others) is pretty sweet and it has all the new bells and whistles (top filling, restrict able juice flow, and additional top flowing air holes). But that's not out yet and I'm not sure in diameter but I've heard good things about the normal Herekles and that is 22mm, don't have one myself though.