Don't get lead blankets. Lead is toxic, so prolonged exposure to it is not a good idea. I suggest instead a futon style mattress. Some of those don't have the springs of regular mattresses, rather they are more old fashioned in composition. They do have some weight to them, but are more flexible than a regular mattress, so this may work. I really think this may help you. However, it will be rather warm in hot or warm weather. I suggest you go with weighted blankets in warm/hot weather, and use the flexible futon mattress for when it's colder.
Question: How high is the bottom of your sofa from the floor, so that you are able to fit under it? I don't know of anyone other than a very small child or pet, who would be able to fit under a sofa. Or are you just lying on the sofa itself, under the seat cushions?
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau