Yeah, toilet paper is really good. A lot of people are too overly cautious, but that isn't a bad thing, just not needed.
use a cleaning solution that leaves no residue is always a good thing. I've used acetone, a thinner use for cleaning up fibre-glass model constructions.
Here's the thing,
Thermal paste has different qualities, I use Arctic Silver 5, a high density polysynthetic silver supposedly 90% (going by a what a sales rep once told me). So about 10% isn't helpful to the conduction anyway. noway the trace (if any) left by your cleaning method will significantly alter that ratio to any serious degree.
On the other hand, you could use a cheap and nasty thermal paste with a density and thereby a conductive ratio that is much less. You might have read about others wanting to remove that stuff that gets caked on, its the white stuff that is difficult to get off. That stuff is an example of the cheap and nasty one, used in those mass produce home pc's by HP and the like. seems to serve the masses ok, so no need to be overly cautious.
recommend you use the good paste though.