How to choose no mattress sofa bed mechanism?

The different function requires different mechanisms for no mattress catagory.

1. Click clack futon mechanism for backrest adjustment.Zero wall or Non-zero wall function?How many stops?And whether has the storage function?

2. Pop up sofa bed mechanisms work like trundle function.There are one-stage for side sleeper sofa,two-stage and three-stage for full length of sofa beds.

3. Pull-out sofa bed mechanisms work similar to folded mechanism but have no separated mattress,they also have one-stage,two-stage and three-stage function differences.

4. Sliding sofa bed mechanisms are driven by body or motors,and different size to fit chair bed,full size queen size and king size sofa bed,and sectional or corner sofa bed.

5. Adjustable sofa bed mechanisms work like adjustable bed with many positions,the differences between adjustable sofa bed and adjustable bed are the length in close position and totally different concept of construction.