65W sounds like quite a bit of power for a heated scarf, but I've never made / used one so I wouldn't really know if that's overkill. Presumably you've calculated how hot this thing is going to get?
An LC filter prior to the PWM switch would limit the ripple that your PSU would see but it would need to be designed appropriately.
Polly fuses are very common in low power consumer electronics, they reset once they've cooled down.
a varnish or similar coating stop the wire shorting - keeping in mind you don't want this to get to 200Deg, so most common varnished would be fine.
I would be very concerned that the wool could catch fire