Sounds like you need the Japanese futon life. No frame, so there’s no weight limit. Just two futons, when not in use you fold them and stack them. More on reddit.com

It exists. Search for a twin to king (two twins together is a king) pop up trundle. More on reddit.com

u/MagnusRaptor , you must add a comment in this post before anyone will see it. Your comment MUST include the word "searched" and detail what searches you've done. Your post will not be visible until you do so. Your inbox should have more details or here are general instructions . Supply as many details as you can. These include, if applicable, but are not limited to: size, origin (store, geographic location, country), age/year acquired, and any writing on the item. Additional pictures can be added as a comment in this post. If you are actively asking for help searching for this elsewhere - another sub or website - link to that search as well to avoid duplicating efforts. Remember to reply Found! (include the exclamation point) to the comment that gives the answer. If looking for an item to purchase, do not click on links sent to you in private messages, and report such to the moderators. For all participants, remember that all comments must be civil and helpful toward finding an answer. Jokes and unhelpful responses will earn you a ban, even on the first instance. If you see any comments that violate this rule, please report them. I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns. More on reddit.com

Late post, but im doing it for the archives and google searchers. I have looked at every corner of the internet and spent 2 weeks nonstop looking at daybeds for my guest room. Birch Lane (higher end brand of Wayfair) is the ONLY strong solid wood day bed I found w trundle (unless you spend $$$$ w an Amish store). The SKU is CDCH1056. It's weight capacity is something like 700 lbs for the bed and 300 lbs for the trundle. Pricey at around $8-900 but again, it's the only bed you can find online boasting that weight capacity. Everything else is flimsy fake wood. I also liked that the bed can take 10" thick mattresses while the other flimsy daybeds only took 8". Good luck More on reddit.com