u could have hot water bottle if get a ?jam thermometer and check temperature from that? oh I see what you mean, it's holding the thing.
best thing I bought was plug in heat pad on a whim, one of my oldies used to clean for recommended it, can wrap round knee if hurts, pop it round a bolster cushion for small of back, even slap it on shoulders. Must dig it out again lol
that and leccy blankets don't cost much to run apparently, bit like a slow cooker, is just a trickle of electricity..
yes catty is warm but he doesn't always settle on lap. loves to dig his elbows in my sore points (fibromyalgia)