for what it's worth, a MOSFET is not necessary for a touch switch, nor is it ideal, in most cases.
The MOSFET switch requires the user to complete the circuit via 2 contacts. Works well with a damp finger, or humid environment, but could cause problems otherwise.
A better alternative is a capacitive touch sensor, using one of
These.
It can be tuned to
sense your finger through the case, requiring no external contacts, although haven't gotten mine to that point yet, still have a
sense electrode on the exterior (just wanted to make sure it would work).
You could either use it to control a MOSFET for a 3.7v
mod, or a control pin on a 5v mod.
I have not had any problems with it that weren't design induced (read: user error)