Hello, my kitty is getting on in years, a little arthritic, and I would like to get her a heated mat. She has some mobility issues and I think a mat would be best as she wouldn't have to climb over anything. I am wondering what peoples' experiences have been with plug-in style vs "self warming" mats. Also any specific recommendations would be great. I would consider getting a larger mat so both of the kitties can use it. Thanks in advance!