Here is a pic from Stickley’s catalog of the Morris chair I am working to finish.  Stickley offers two ways of upholstering the seat, one as shown in the pic, the other way as a loose cushion.

As shown, the upholstering is done right to the seat frame, which is a mortise and tenon 4-piece affair, fitted with a crisscross lattice of webbing.  The seat with its frame bottom then bears on perimeter ledger strips screwed to the chair frame.

In the loose cushion model, there is a frame with webbing, that is upholstered at its top with a leather panel and perimeter edging.  This, to the top of the frame only.  Again, the frame fits to the chair frame as above, and atop this sits a square-edged loose cushion.

If you have built one of these, what was your preference, and why?

Here is a pic of a chair with the loose cushion seat.  Not the Stickley, but the cushion method is as described here.