I have a little space heater in my room that boosts the temperature up a bit, but it's so expensive to leave it on permanently. I'm considering getting an extra UTH, although I've just checked and the hot side is now up to around 91F.
Cold side is still very low, more than likely because it's Winter in the UK at the moment. It seems excessive to get a ceramic heater or a bulb. Going to have to get the space heater out and see if that helps!
EDIT: I've also got the tub set up on my desk quite close to the window, so I'm considering moving it further away from there to see if that helps.