Replace it.
Our Crossroads fiver had a hide-a-bed "couch" that was really more like an oversized loveseat. It, too, was sinking and would swallow you up. We took it out and replaced it with a wall-away style reclining loveseat. Clearance purchase at furniture store - I think it was $500 or so. Weighed less than the couch that came with the fiver, and was easier to get in the door because the back came off.
When we sold the fiver, we pulled the reclining loveseat out and kept it, because it was so comfortable. Replaced it with another purchase from the clearance section of a furniture store - spent $125 on a middle section (no ends) of an extremely expensive sectional couch. It had been damaged during delivery - a small hole was torn in the fabric in the back. Couldn't tell when it was installed. It filled the space perfectly, with about 1/4" clearance on each end - put some pillows at the ends for armrests and it was good to go. It was SOOOO comfortable - even moreso than the reclining loveseat we took out.
Shop around. Take measurements of the space you need to fill, and the doors you need to get thru. You can often find better quality, more comfortable furniture for not much money!