how to tell if cat is warm enough (2 seniors)

hi
i have 2 elderly cats and i am concerned about them being warm enough
but i can't afford for my heating bills to go thru the roof either

how can i tell if they are warm enough?
if they are tightly rolled in a ball, does this mean they are cold?

what temp should i keep my house at?

thanks for any ideas!

Well as far as I know , cats are cold when rolled up and when they cover the head with their tails . You can buy a heat pad for them , cover the pad up with a nice towel and keep it at low . That's what I do . I got me a heating pad fom wal-mart for about $ 10 dollars and I keep it all year round going for my cats . But you need to check on the pad every day . You also just can uses it over night to keep them warm when most needet .