It’s still a folding one but the one that came with my teardrop has been extremely comfortable. Milliard Tri-Fold Foam Folding Mattress and Sofa Bed for Guests (Queen) https://www.amazon.com/dp/B08FBJS2DZ/ref=cm_sw_r_cp_api_glt_fabc_WQE4D1P18MSJ94N9JYA7
We have this Milliard foam folding mattress that is pretty great. Milliard Tri-Fold It has a lot of potential uses - soft play space for babies, folds up into a couch or lounger shape, fun for making forts - and we have used it for cosleeping for a few days when waiting for a new bed to be delivered. My mom actually prefers to sleep on it when she visits. It’s firm but not too uncomfortable. It also comes in a queen or king size. It would likely be too big to travel with but you could order it to their house; might even be something your family would be glad to have around!
Milliard Tri-Fold Foam Folding Mattress and Sofa Bed for Guests (Queen) https://www.amazon.com/dp/B08FBJS2DZ/ref=cm_sw_r_cp_api_i_EFYWHSFFGMPRSD1TVKEJ
My one year old has a floor bed. It’s great. We can lay with them when needed, then leave the room quietly. We have a monitor and go in when they wake up. It’s been a lifesaver since they refused to sleep in their crib. It folds into a couch so we can repurpose later when/if needed. Links below.
Mattress: Milliard Tri-Fold Foam Folding Mattress and Sofa Bed for Guests (Queen) https://www.amazon.com/dp/B08FBJS2DZ/ref=cm_sw_r_cp_api_glt_fabc_4EJW8012DWJ61B1RCXS9?_encoding=UTF8&psc=1
Sheet: Stretch Queen Fitted Sheet Only - Jersey Knit & Ultra Soft, Non-Slip and Snug Fit for Queen, Queen XL or RV Short Queen Size Mattress (Deep: 5" to 16") - Beige https://www.amazon.com/dp/B08BHWL66J/ref=cm_sw_r_cp_api_glt_fabc_0KEEDTM30T6W6757B3Y8?_encoding=UTF8&psc=1