I know your pain, as I was once in that situation and there's no getting comfortable lying down on the sofa with a keyboard!
I, too, searched for some sort of PC keyboard remote, but no luck. However, I did find a practical solution--similar but much better than the wireless keyboard I was using on my sofa...I ended up buying myself a mini keyboard, the Logitech diNovo Mini. Check it out:
It fits into the palm of your hand and has backlit keys. It works really great and is definitely much more comfortable to lie down with than a full-sized keyboard!