Power Line Carrier
You might want to use a capacitor-blocked, high frequency
transformer because Job 1 is safety - galvanic isolation
of a few thousand volts is not only a good idea, but would be
an absolute requirement for getting your product (if it were
real life) certified.
Tune your LC, primary inductance (and reflected secondary)
and capacitor to your 100kHz carrier tone. You can post-filter
additionally in the signal processing chain.
Going this way with a "sniffer" across the mains, probably
will give you more signal than trying to pul it off the secondary
of some "big iron" 60Hz power transformer.