I used to tell my guests who asked Go to Sam's Club, buy the most expensive mattress they have in the store, and bring it home. When we started decades ago Sam's Club had a large selection of mattresses in their stores. The last time I went there specifically looking for a mattress they had a very limited selection of fairly inexpensive products that were of lesser quality than the mattress I wanted replace. Their choices in-store are very limited, but if you go on line they've got mattresses that range form $399 to $4999. I ordered something in the $1500 range.

I want something that is going to last, and will make my guests comfortable. Look for something with a high coil count, with inner springs. While "memory foam" sounds like a great selling point, I've read too many reviews from people who find they sleep too hot, so I avoid them. Something with a medium firmness will give your guests the support they need. A "Pillow-Top" design gives an added layer of plushness. Something that is becoming harder to find is a "Double Pillow-Top." I like those because you can flip the mattress over every few months to help extend its life and minimize wear points. With a single pillow-top you can only rotate the mattress from the head-board to the foot-board.

Also, don't forget a good quality mattress cover/pad that you can remove and wash between guests.