It's hard to believe that no one's posted at least one suggestion yet... I guess everyone is out getting their last minute shopping done, it's been slow just about every forum I visit.
I don't know if I have any good suggestions or not... I'll mention a few that are sized about right but I've only tried one and I'm not blown away with it.
I just got the Smok XPro BT50 yesterday ... my initial thoughts are posted here
http://vapingunderground.com/threads/smok-xpro-bt50.42120/
It works ok so far ( one day isn't a big test for how it holds up )... I'm just not blown away with it and it's one big feature is iffy at best. It's also got rattly buttons which most will be bothered by including myself. It's bluetooth turns off by itself so when firing... there is a delay. I'll let you read the rest of my post for more info. I will mention that the 510 sits in a shallow depression on the BT50 but the Subtank still works fine without the need for the 22mm adapter they provide.
There is a new Smok XPro M50 without BT... but it's a 22mm wide device and like the following I'll be mentioning, I haven't used it.
Here is a shot of the Subtank sitting on it... and a couple of other mods I've got including the VS DNA 30
Others to look into but I can't say anything about...
There are a few of the Hana style mods including one 50w that is wide enough. There are also a few that are narrower, so pay attention to the details.
There is also some new wood mods by LUXYOUN found on both FastTech and FocalEcig's websites... they are available in 30w, 50w, 100w and 150w. They are 26mm wide. These are single 18650 mods which makes me question the 100w and 150w since the battery won't last long using anything close to the max power on those. The reviews I've seen/read were encouraging although no one liked the big name badge on it. I've heard they use a YiHi SX1000 chip on it... I think that is an error and what they are referring to is the board model it's on... I think it ( at least the 100w ) uses a SX350 chip on it, but this is a guess on my part. I have one on order ( the 100w )... but it hasn't yet shipped.
Everything else I looked at just to give you things to check out... were not wide enough but perhaps those will get you started.