Old padded physio table or the like. (IP1)

I need to do exercises that require lying on the floor. Painful knees mean I can’t do that anymore, what I need is a table at chair height, or similar, that I can just get onto, like into a bed. Tried a plank across the bed, but that’s too hard; need a lightly padded something that’s long enough. If anyone has one they are getting rid of, I’d be really grateful to try it. Thank you.