I don't usually recommend Chinese made goods but as it is good for cats I will make an exception.
Alice loves this bed. They are quite firm but not rock hard - good for supporting dodgy joints?
Alice moved just now and it is really toasty where she has been lying. They cost next to nothing to run (about £2 for a whole winter) the sides are flat at the top so they are good for cats to sit up and observe when they aren't sleeping
. I just use £1 fleeces so the heat still goes through but I can change them every few days and still keep the bed clean - although you can slide out the heat pad and wash if needed (they are suedette so not the nicest feel for cats to lie directly on top of.
I can't praise them enough - and barely cost more than a decent regular bed. They are very well made and also come with a car lighter attachment of you want to use them in the car.
This is where I got mine - the cheapest I have seen them. A proper supplier
http://cgi.ebay.co.uk/Luxury-Heated-Pet-Bed-for-Dogs-and-Cats-Small_W0QQitemZ300262502617QQcmdZViewItem?hash=item300262502617&_trkparms=72%3A1301|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14
I think the link is showing a young puppy in a medium bed even though they are selling a small
Word of warning. They are quite small so you might want to get a medium (they cost more) if you have a large cat. You can see in the picture, this is a very young cat.