On Monday, January 11, 2021 at 10:16:25 PM UTC-5, Sonny wrote:
On Monday, January 11, 2021 at 6:29:31 PM UTC-6, DerbyDad03 wrote:

I'm not quite sure I understand the process completely, but this sounds kind
of permanent, right? Permanent as in the cushions can't be easily removed
for vacuuming, etc.?

For what it's worth, the couch is sort of like this one, where the loose seat cushions
kind of get shoved under the permanently attached back cushions.

https://i.imgur.com/JJV8Fpf.jpg
Info: The surface under the cushions is called the decking.

Many sofa cushions have semi-circle rings on the cushions' sides, at/near the back . These rings are attached to clips on the inside of the arms.... tucked down into the sides of the sofa between the arms and decking. These attachments hold the cushion in place. The ring is sewn in place via a strip of fabric. The clips are attached to elastic bands that are stapled to the sofa frame, tucked down inisde and below the arms and decking crevice. The clip allows for removing the cushion when needed.

The button or wood strip attachment can be similarly applied to the ply. The string can be looped and the ply aspect can have an "S" hook type of releasing attachment to hook onto the string loop, hence the cushion can be easily removed. This method is DIY, quick and easy, doesn't require sewing anything (except for running the button's/wood's string through the back of the cushion fabric. It's another form of the typical upholstery ring-clip attachment, but a DIYer alternative.

As per your pic, I have a similar sofa in the shop right now. I'll get some pics of the button and/or wood strip procedure and post..... hopefully this evening, depends on how fast/convenient I can do it.
Sonny

The clip and loop explanation makes more sense to me than your previous suggestion. Pictures would be nice though. ;-)