I use a quilt and a bedsheet on top. I hate electric blankets. If I'm with someone else, just a quilt will do - unless it's exceptionally cold like down south or in Melbourne. I sleep au naturale but on some really cold nights, it's on with the tracksuit pants.
One of the best, cheapest and most under rated things has to be the humble hot water bottle! Coles sells them for $8! Just one filled up is great and even in the morning it's still warm. You don't have to sleep next to it, just put it down the end of the bed. MAJOR CAUTION NOTE: BE CAREFUL WHEN FILLING UP THE HOT WAT BOT - FILL IT SLOWLY IN A NARROW STREAM FROM THE KETTLE. WHATEVER YOU DO, DON'T USE A FUNNEL OR YOU'LL SCALD YOUR HANDS.
I'm follicle-ly challenged (read "bald") on top so to avoid waking up with a head cold I sleep with my dockers beanie on!
When I was a student years ago, I used to sleep in a sleepout which could be quite cold and I had a kero heater on in the room - a bit of a no-no I discovered later in life. Still it did the job and if you take necessary precautions, I'd still do it depending.
A friend of mine, also a student, erected a largish tent in her bedroom over her mattress! And I slept in it once and frankly it did the job because your body heat is contained in a small space. I'm buying a small van (not a campervan) next year because I want to spend more time going down south on the cheap. It'll be interesting if I can stand cold nights with several blankets in a confined space with my own body warmth! Go the hotty watty botty!