This can be placed under the mattress, not recommended under a boxspring.
No, this can't be used in a queen size sleeper sofa mattress.
The weight capacity for this item is 440 lbs.
No this surface is too hard for exercise purposes
The black striping holds the board segments together and can adjust to size folding
Yes I think that would work fine
Yes I used these to replace my boxspring however the framework needs to be very strong throughout to support the weight of boards, mattress, and person sleeping