I used to use optiflex which was a transparent film
But more recently have used hypafix as an overtape when sensors are lifting a little. I get it as a roll online, and just cut off patches/strips to suit.
It’s important not to tape the sensor down too firmly I think (which can result in a sort of extended ‘compression low’)
Abbott also recommend for Freestyle Libre that the centra hole should always remain uncovered, so that the skin under the sensor can breathe.