Mattresses can be made of a variety of materials, with two primary advantages over modern mattresses: (1) they can be non-toxic, and (2) less expensive (but some are more expensive). Permies has a discussion on alternative mattresses and most of these notes are digested from that discussion and related links.
- Making a straw mattress is easy and inexpensive. People report that the result is comfortable as well. This discussion on permies.com details one person’s experience with others adding their knowledge. Some people make their own mattress covers (called “ticks” in old times) for holding the straw or other plant materials while others (see this person) simply buy a mattress cover and stuff it.
- Natural latex (expensive but long-lasting and comfortable)
- Bedstraw (Galium aparine). Some people are allergic to this.
- “As for stuffing your pods, galium odoratum and galium verum are traditional for stuffing mattresses, and seem like they’d be more comfortable than straw.” (source)
- Wool (seconds, short cuts, and coarse edges–free reject stuff). Wool mattresses.
- Feathers
- Horsehair
- Cotton (including blue-jean insulation)
- Sheepskins (“a couple layers are surprisingly comfortable and warm, even on top of cold cement”) or other animal hides (e.g., caribou). “Sheepskins on plywood are warm and comfy”
- Buckwheat hulls (use this kit). Wheat bran as a possible alternative.
Beds
“I got a kingsize cotton mattress zip cover (mite/bedbug resistant weave) on eBay for $30, sewed a couple sheets into sacks, stuffed one with wild prairie hay [note: some people emphasize using straw not hay] I stole from university field bales, another with buckwheat hulls, and the rest with sheep wool from an etsy seller. if I did it again I’d go sheep wool and hay, skip the hulls (very heavy and pack down easily) and get the natural latex to help keep it uniform flat. all under $300 
sheep wool is amazing.” (source)
Rope beds or beautiful charpoys.