Hey Moonshadow,
Welcome to our mattress forum :).
Thanks for the post, I totally understand the āusesā of this in the family/rec room. There are a few diff ways you could do this. But let me give you a couple of quick examples that would work great for this bed. If you wanted to use latex and keep in at 6" total, then I would use two 3" pieces. The bottom 3" would be āfirmā and the top would be āmediumāā¦still great for sleeping but higher densities for lots of kids and other sitting on the bed. Something like 3" 36-40 ILD and 3" of 28 ild. If this is too expensive them you may use 3" poly foam 1.8lb or greater on the bottom and then put the 28 ILD latex on top of the foam. Any of the latex experts on our mattress membership listing would have the latex and the zipper covers for this.
My thoughts are very general, you could use more or less firm latex on any part of this, especially of its mostly pre-teens and then teens sleeping on it. For Durability reasons and used as a sitting place, I would tend to stay above 24 or above ild on the top layer. If you were to go with 8" ābedā then I would find 6" 36 or more for the bottom and then put 2" of 28 on top fo that. Polyfoam could be used for the bottom 6" of this as well.
Hope this helps, I would be glad to answer any other questions you may have.
Thanks
Sensei