Keeping your cats warm with cat radiator beds will keep them happy, as well. There are lots of ways to keep them warm, but this will probably be a favorite.
When left out in the rain, they will search and search for a warm, safe spot. One that is dry and quiet, if they can possibly find that. Nothing will compare to being inside, where it is safe and warm, but sometimes they have to settle for going under the house instead of inside it. They do what they need to do to survive.
When you want to show appreciation for the kitty, just get him a radiator bed. It fits comfortably over the radiator to stay very close to the warmth of it. It is sturdy so that when your cat jumps in it, it does not move or let go. And best of all, he will love you for it.
They are usually made of either plush or other fabric that your kitten will adore. It is removable from the actual bed frame, sometimes with a zipper underneath, and it is washable. The plush is generally short, so that it does not gather a lot of fur and dander. And they come in a variety of different colors, as well. They come in some sorted shapes, such as a kind of cradle, or a plain flat surface. Either way, your animal snuggles in and keeps warm in it.
And for the larger cat, no worries. The radiator bed is sturdy and will not move when your big cat jumps in it. The big guy needs a comfy place to sleep, too, after all.
And if you do not have a radiator, do not worry. There are other pet beds that do the trick nicely. The infrared heating bed plugs into the wall and heats up, so that you can just place a soft fabric over it and you have a heated bed for the kitty. Or he can warm up a self-heating pad all by himself. It heats up with the animal body temperature.
There are also other types of pet heaters, such as those found in kennels, and again, you would need to cover them with a towel or other soft fabric to keep the pet heated. They are also fine for the home, and they have an element that maintains a certain set temperature. They are also waterproof, although they should never be submerged into water. And then there is the microwavable pet bed that can be used out of doors, as well as indoors. You just pop them in the microwave for a few minutes and they will stay warm for up to 12 hours. It comes with a fleece covering.
There are so many ways to keep your kitty warm. His favorite is probably just being in your arms. But for those months where the radiator is on full blast, you may want to look into cat radiator beds.