Personally I wouldn't. The safety rules for cots are strict for a reason and a couch just doesn't meet those standards. I'd be more inclined to get an old school padded cot bumpers.
That is my concern- that she would get her face all squished into the side of the couch... I have one bumper in the cot, but honestly it does nothing, its catch 22, anything soft and squishy enough to pad it well, becomes like a couch and is a suffocation hazard.
I dont know what we will do, i just know i am sick of getting up ten times a night coz she has bumped her head lol!! I think she wriggles too much to put a matress on the floor, she would just roll off that and wake up coz she isnt on a bed lol!! Although we have spare double bed.. maybe the double bed matress on the floor.. lol she would have plenty of rolling room there!!! But then she would be free to wake up and crawl anywhere... and we have a heater on in the hallway that isnt "free baby proof" (it only goes on when she is alseep) Maybe i just have to build a giant structure around the matress.. lol the playpen for sides maybe to keep her in!! The couch could go against it so its the hard-ish back not the soft squishy bit!! hmmmm... It wont look pretty, but it might save our sleep!!!
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