I'm pretty sure you can use the switch assembly that is in the RES interface with the standard atomizer interface, I'm fairly confident that they're the same (just push it out from the atomizer end and don't forget the o-ring). This would save you a few bucks if you just had to
buy the interface with no switch ;-) I'm sure TmeisT will be along to confirm whether the switch assembly is the same or not
One thing to note, there are now two different tensions for the switch mechanisms, the newer one being a little bit lighter spring. So if you wanted the
new switch then you'd need to get the interface with switch (then you'd also have both switches).
Sorry to hear the RES isn't agreeing with you