He did add, pee in a dedicated bottle with a secure lid and put that in the bottom of the bag to warm it up as an extreme way to stay warm...your call on that one!
Cold hands, you have riding gloves right? Wear them, do you also carry wet weather gloves, these will hold in the heat better...or of course as above a dedicated pair of warmer thicker gloves just for sleeping in.
Cold head, get a beanie, make sure it covers your ears, most of the heat you gain in a sleeping bag will be lost out of the top of your head...cover it. If your face gets cold, try a balaclava, and a beanie over it, if it's really bad.
Just not happy with your bag overall but can't afford another $300 to $500 for a top of the line new one.
Look for insulated blankets, they start around $25, it only needs to cover your upside, and again pack size is very small for the additional heat they generate
If you are thinking how will I keep it around my feet when it's cold? Rubber band or paracord tied around it will make the end into a pocketed area.
Additional inner sheet style bags offer little in the way of warmth and if you move around in your sleep you'll find yourself getting tangled and having to undo the sleeping bag to untangle yourself, letting all the warmth out.
other options and also very small pack size, good to keep one in your hydration pack are emergency blankets or bags, usually less than $10, they hold a lot of heat with mylar type materials, but be warned they DO NOT breathe so if you get too hot then there will be a lot of moisture