Fire alarm question, cont'd?
Probably a duvet; they're filled with down and are very light and warm. You can get them at most department stores. Try Quilts Etc if you have one where you live.
If you have a standard knob set, or lever set, then it has the lock built into it - so yes, the easiest method would be to change it out. You could take the new lock to a locksmith, and he could make it match your existing keys, if you wanted to. If you have a separate handle and lock (called 'handle sets), then you could change only the handle without changing the lock itself. If the deadbolt is looking tatty too though, then it means the same situation as with the knob set - you can have the new lock re-keyed to match the old. Have Fun
A comforter, quilt or maybe a throw. I camp so I know from sleeping bags. They are much like a comforter or quilt The best bag or comforter will have some sort of quilt and will have a fill. The best fills are Thinsulate, Hollowfill, polyester and down. Down is more expensive and is hard to clean and (not that you would have to worry about this) but if it gets wet it stops insulating. Thinsulate and Hollowfill work even when wet and are easier to clean. Polyester is common but not as good. The other thing to do is consider spending the money on wool blankets as most are acrylic and are not as good. Wool is heavier but trouble to clean and It also is fire resistant. None of the others are unless they are treated.
