My only concern would be making sure it does not get too warm, and I would not ever leave it on if I left. In the past, I have used human heating pads for senior/sickly cats, and they definitely enjoyed them. It just always made me a little nervous. I did have an incident where one had a short (I guess) and flipped a breaker. No damage done other than nearly giving me a heart attack.
Willow is 16, and I have noticed a little stiffness in her back legs, and she is a little thing of just barely 7 pounds. Since it is getting colder (and I keep the house pretty cool), I want to make sure she has a warm spot, so I ordered a self-warming mat. It should be here by mid-week. I can let you know how it works out, if you are interested. Here is the one I ordered:
https://www.chewy.com/kh-pet-products-self-warming-pet-pad/dp/128078