Cat heating pads?

Kidsandliz thought this was worth mentioning said

So my ancient cats (turning 17, all three of them) are bony old souls, feeling like little, hollow boned birds when you pick them up… One is really underweight (many, many, many vet visits recently) and the other 2 are just old age skinny. In this drafty dump (10+ degree difference between different rooms, drafts move the miniblinds…) they need several warm spots to curl up in.

Any suggestions for good, no auto off, has a large area of heat (the one I saw in person at a pet store had about a 8" square heat pad in a 12"x22" or so pad - stupid the rest of it wasn’t heated), safe for kitties heating pads or beds that won’t break the bank?