This was gonna be my answer. I got one a few weeks ago after using a kotatsu heated table at a traditional hotel in the mountains here in Japan.
There's life before one has experienced a kotatsu, and life after.
#snugLife
This is really true. I spent my day in Shirakawa-go in the snow and when I got to the hotel it was freezing. I put my legs under the table and... WOW!!
My wife just wears slippers. They work in the entire house.
Can you share which one you have?
I legitimately don't remember. Just search "foot heating pad" on Amazon.