Our idea of relaxing and "sinking" into a thickly cushioned furniture piece would be uncomfortable and possibly painful to them. The clothing and the physical posture their bodies are used to just does not encourage a curved spine. I have found in wearing this clothing every day for my job, I either perch upon the edge of a chair or lean in order to recline on certain types of furniture. This image from Hogarth's Marriage a-la-Mode series shows a group in repose in much the same manner. That doesn't mean there wasn't furniture or cushioning we would consider comfortable even today. The portrait of La Liseuse from 1776 shows a large pillow behind her back as she lounges in the early morning before properly dressing. This may not have been built into the chair, thus would not appear in museum settings. Turkish influence was also very prevalent and can be found in items like floor cushions as well. When it comes to furniture, they required a different style than we do today, but we also have to remember that it is often the wooden portion of the pieces that survives, while fabric, pillows, and padding often rot. It may not always be a truly balanced display of surviving pieces.