Saggy couch pillows..and how to clean couch?

Put several double face velcrow between the back of cushions. Stuff the pillows with stuffing which you can buy at a craft store.

Sooo . . . to clean the sofa - call someone and pay them to clean it professionally for you OR you can take your chances and clean it yourself, the removable parts anyway. I remember watching in awe the first time I seen my Bestie's Mom washing her cushion covers. Of course I had to satisfy my curiosity. She said she washed them in cool/room temperature water like you would for regular laundry and then she air dried them and returned them to the sofa and loveseat. I dunno if you remember those very 'busy' patterned sofas from the past with the kind of 'velvet-like' fabric, but that is what her fabric was.

As for the sagginess in the back there - it is happening because there is a shortage of stuffing. A few options there. You could open them up and add some. I dunno where your zippers are located but you could also do something to 'beef' them up a bit by adding some actual foam cut to the same size and shape as cushion. Folding foam and then opening it once it is inside is the easiest way to do it. Then be sure to add 'fluffy' stuffing or use what's in there to give it back the 'pillowiness' look. Just remember to kind of 'overstuff' them as they tend to squish down with time (insert the photo you provided).

I am a professional at pretty much nothing. But I'm cheap and like to do things for myself. I, personally, would do the room temp wash and foam and stuff methods if it were my sofa. Good luck to you! Hope I got the hamster back on the wheel for you with some ideas.

Rent a unit used for cleaning carpets just make sure it includes attachments to clean furniture too.

Here's a post that fixes just that problem! https://www.hometalk.com/diy/living-room/furniture/how-to-make-a-saggy-sofa-look-brand-new-4156124

Here's a post that might help you - https://chascrazycreations.com/cleaning-yellowing-pillows-and-more/