Some people are more prone to hypothermia than others. This is not just your imagination, nor does it make you a wimp. It's simply the way you're built. If this applies to you, admit it, recognize that it means making changes in how you camp and what you need to take to be comfortable, and make those changes. If you don't, camping will be a miserable experience for you. Or you may give it up altogether.
The tips here are for everyone camping in cold or wet weather, but will apply any time of year to those who are prone to getting chilled.
A medieval way of staying warm is to make yourself a 4 poster bed with a top and side curtains, so that the space immediately around you as you sleep is kept warm by your body heat. Any kind of tourney bed or cot will get you off the ground, which is a prime source of heat loss. And an added benefit of a four poster is that you can cover the bed with a waterproof sheet, so that even if your tent or pavilion leaks, at least your bed, and you, stay dry.
We have a 4 poster tourney bed that is easy to make and set up, and it probably takes us about 10 minutes to set it up.
Put an extra ground sheet under your tent. MAKE SURE THIS DOES NOT STICK OUT FROM THE EDGE OF YOUR TENT BY ANY AMOUNT!! The slightest bit of ground sheet sticking out will collect moisture and direct it under your tent, making everything damp and cold. If it's really raining hard, dig a shallow trench all around your tent, about 3 inches out from the edge of your tent, and a few inches deep. This will collect the rain that would otherwise be under you.
On top of your tent floor, put another ground sheet. Garbage bags will do, but they're slippery. On some tent floors, this can be a problem.
On top of the ground sheet, place something that will insulate your mattress, whatever it is, from the ground. I used bubble pack designed for camping. Then I put down my foam mattress. On top of that, I put an acrylic blanket. It MUST be acrylic or similar synthetic. NOT wool! Wool wicks moisture from your body. This will create the very problem you're trying to avoid. You need a vapour barrier here. You can get cheap "Camper" blankets for about $4 or so at stores that cater to campers, especially department stores. Or any emergency blanket will do, the Mylar or the fuzzy type.
Now you can make your bed. The Boy Scout/Girl Guide rule is: two layers below for every one above. You can use a sleeping bag, with at least one extra blanket or comforter underneath (usually whatever you use as a vapour barrier is not something you want to sleep right on top of). Or you can make a proper bed with sheets. Whatever works for you.
If you insist on wearing something to bed, keep it dry, in a sealed tub or a garbage bag. Nothing chills you faster than dampness. Wool is great for sleeping socks. And wear your sleep socks only for sleeping. Don't be tempted to leave them on in the morning. Take them off and put clean socks on for daytime. Dirty socks make your feet cold. And for most people, if their feet are cold, they're cold.
Consider a nightcap. A stretchy toque or even a coif (like a giant baby bonnet for grownups that ties under the chin) will reduce heat loss from your head. Nightcaps were not just a fashion statement!
Hot water bottles are a good idea. Spend the extra few bucks to get good quality ones. Don't overfill them. Fill them about two thirds full, then get most of the air out, which will keep it warmer longer, and also reduce the pressure. The last thing you want is a hot water bottle bursting in your bed halfway through the night!
Bring 2 or 3 hot water bottles, fill them with boiling water, and place them in various spots in your bed about half an hour before you plan to retire. This will warm things up for you.
I have no experience with those chemical heater things you can buy to keep your hands and feet warm in winter. They cost more than a hot water bottle (a buck or two per unit), but they're easier to use than boiling water and filling a hot water bottle, and easier to pack. I've heard they work well.
Avoid alcohol if possible before you retire. While it's a big part of the SCA experience for many, it can make you do foolish things, like go walking without your cloak, or fall asleep exposed to the cold. It reduces your judgement, and it also dilates the blood vessels on the outside of your body, making you lose body heat. A drink may make you FEEL warmer, but this is an illusion caused by the blood rushing to your face and hands.
Try to have a warm drink before you go to bed. While some drinks, such as cocoa or tea, may have a diuretic effect (and those midnight rambles to the privy do nothing to make you feel warm at night), but a cup of soup or even plain hot water can help increase your core temperature.
A bit of mild exercise, such as a stroll in the immediate area of your encampment, can also increase your temperature a bit. But vigorous exercise that gets your heart pumping will keep you awake.
1. Keep your bedding and sleeping clothes dry.
2. Try to get your bed off the ground. If you can't, insulate yourself from the ground. At least one layer of vapour barrier between you and your mattress, and two layers of bedding below for every one on top.
3. Consider wearing something on your head.
4. Heaters are probably a bad thing. If you have access to hot or boiling water, hot water bottles can keep your bed warm and help you adjust to the bed. Or chemical heaters can work.
5. Have a warm drink or a bit of exercise before turning in, to raise your temperature. But avoid alcohol.
