Valentina sleeps on a twin bed. We had to cover it with a washable material to keep the smell out and so her claws didnt make holes in it. She has been sleeping on it for about 5 years and she loves it. I get on it with her sometimes.She freaks out when I take the blankets off to wash them. But she is so excited when I put the blankets back on lol. The main reason I decided to use the twin mattress is because there weren't any beds large enough for her. She likes to sleep all stretched out. When she does stretch out the mattress is almost the perfect length from her nose to tail.She is a very long Dog. Also most of the beds we found had washable covers but the smell still permeated the insides of the bed. And the fabric was never strong enough to hold up to her weight and claws. I would buy her a $120 bed just to have her claws rip the fabric a couple of weeks later. I am somewhat obsessed with keeping the Dog beds clean so we covered the mattress with a material used to cover boat seats. It worked great! Over the that I use a fitted sheet and then a comforter. I wash them very often. They get stinky fast and it can smell like a pet store in here lol! I even have a separate washer and dryer in my garage only for the Dog's bedding. When I washed them in the family washer too much Dog hair got in there and it was hard to get out. Big clumps of it got stuck places and it grossed me out so I have one just for them. Thank goodness for that because of all that drainage Valentina had after her surgery. I had to wash towels and blankets several times a day! Anyway not sure about the toddler or crib mattress. Maybe for a medium sized Dog it would work just fine. My Doberman would probably do ok on one. They are really firm though. I probably didnt help much but I like this subject because I had such a hard time trying to find an appropriate Dog bed for Valentina.