Your average heating pad is likely to burn the cat.

I used a regular heating pad for my cat.  I put it inside of a fleece
covered pad that I made and kept it on low or warm.  Any warmer seemed too
hot.  My cat liked it.

Sue

A couple of things to try:

--set kitty up with a bed near a heat duct. My older cat spends 6
months a year enjoying warm furnace air.

--Polarfleece is a wonderful fabric that reflects body heat, and they
like the way it feels (mom!). This morning I dragged out two of my PF
throws, and instantly had company.

--If you do go the heating pad route, I would get a timer and set it to
cycle on and off every hour. It'll stay warm enough and has less of a
chance of burning your house down.

YMMV

HTH

--Karen D.