How do I deal with this sweat-soaked bed every night?

I love my boyfriend very much. We're in it for the long haul. But the one thing that drives me crazy the most is his night sweats! Every night since he was a teenager, he's been soaking his sheets all the way down to the mattress (which we still use) in what I find to be particularly smelly sweat! There seems to be no way of avoiding it; he uses a big powerful fan and opens the window in the middle of winter and still he sweats so much that it seeps over onto my side too. It's grosssss!
Are there any good products I can buy to aid me in my fight? We can't afford a new mattress in the size he wants, and a crinkly Plastic Mattress Cover would embarrass him. Maybe a pad, made of some super-absorbent material that I can fit into the washer every morning (unlike our quilt)?
Any other tips from people who also live with sweat-ers? I am at a loss, so I'd appreciate it very much!

MAYBE HIS PROBLEM IS THE AMOUNT OF SUGAR INTAKE HE HAS DURING THE DAY. CHECK INTO IT AND CUT IT DOWN BECAUSE SUGAR WILL MAKE A PERSON SWEAT LIKE HELL AT NIGHT. IF NOT THAT, YOU CAN PURCHASE 2 FT X 2FT ABSORBANT FELT PADS THAT IS SOFT ENOUGH TO PUT UNDER THAT SHEET. YOU CAN GET THOSE AT THE LOWES STORE OR DEPOT OR MENARDS.