@Stacey64
My listing is a guest room in my apartment and I have a super-single size bed which is a size only available in Asia. So in my listing description I just added the dimensions.
• 1 super single sized bed (110×200cm or 43×79in) - mattress is "firm"
I also added that the mattress is firm because of a comment from my 1st guest. She casually mentioned after about a month that the bed was firmer than what she was used to and took a couple days to get used to it, but after a while she found that sleeping on a firm mattress helped to improve minor back pains she used to have. Because I've always prefered a firm mattress, and the one in the guest room is actually not THAT firm in my opinion I was a little surprised but immediately offered to get a topper for the bed but my guest said she was fine and didn't want a topper. She said once she got used to it, she liked the firmer mattress 🙂