This depends on your space and requirements. We recommend choosing a day bed or trundle bed if you have a spare guest room. However, a folding bed arranged in a study or living room will work just as well.
Yes, most trundle beds come in twin and double sizes and are suitable for adults. It's worth checking your bed's maximum weight limit, which will be defined in its manual.
Most trundle bed mattresses come in twin, twin XL or double sizes and should be between 8" and 12" deep.