We have a trundle (typical) with a second twin bed under it that you pull out on castors. It's in our teen's room that doubles as a guest room for us as it has an attached bath.
I personally hate it -
1 - no one likes sleeping on a bed that low to the ground (it's on the floor) and it's a pain to lean over and make
2 - it gets dirty with kid sleeping on it above with slats so has to be thoroughly cleaned before each visit
3 - you have to remove the nightstand and cords (lamps) etc because it pulls out next to the regular bed. This is a pain in a room without a whole lot of room and means rearranging furniture.
I would never buy one again.
What you are asking about (I just wrote that above, in case anyone is interested in those) - my sister has. She has a trundle or daybed (?) that you pull out two twins and it makes a king because they lay side by side. The whole thing converts (you pull it out somehow) and it's very comfortable and you're at bed level.
She loves it. You can buy whatever quality mattress you want as did not come with it and hers does not scream 'bed'. It's in their office. It looks kind of beach house. She has pillows on it to go with their decor so kind of looks like couch. It doesn't have a high headboard in other words.
The bottom has drawers that have the bedding. I would do that. It functions mainly as a really comfy couch for them most of the time. They lay on it and read too and her hubby naps in there. They are probably yours and your hubby's age (kids have left the nest).
They use it several times a year for visitors. They don't have a nightstand right next to it as it's an office so it works.
* Because it's in an office, and no closet in there, the storage underneath - very helpful.