This would be a great idea for a backyard movie night for the kids! Via the Dating Divas. She took a kids inflatable pool like this one, this one, or this larger one, and filled it with pillows and blankets but I would put a memory foam mattress topper in it, then the pillows and blankets. I'll tell you a little secret....see under photo.
I've bought three 4" thick memory foam mattress toppers off Overstock.com and have gotten FIVE out of them! Here's the trick. This memory foam mattress topper is $80.99 sometimes it's more sometimes it's less. But it's always the same price for ALL sizes. This might seem unfair if you're only getting a twin. Here's what I've done....
We bought a king sized one for our bed and I LOVE it. It solved so many issues for me. Now, everytime I get in my bed at night I fall right asleep. It's beyond words. So I wanted to get two for each of the kids beds because sometimes I lay in their bed when they need me to. I didn't want to pay the same price of a king sized mattress for just one twin. So I bought a king size and just cut it in half! It's just foam, not springs. It cuts as easily as bread. And voila! Two mattresses. BTW, the size of two twins side by side are exactly the same size as a king.
Then my mother wanted a twin sized memory foam mattress topper for Christmas. So again, I bought a king, cut in half, gave one to my mother and used the other for myself. Currently we use it on the guest bed but sometimes we remove it, fold it in half and place it in the back of the minivan for drive-in movie theater night. It's the comfiest thing in the world! I love snuggling with the kids on it.
Right now you can save 15% on Overstock using this retailmenot link, meaning you could get a king sized memory foam mattress for only $68.85! But I've literally bought this mattress for $38 with free shipping when all their memory foam was 40% off and I was a club O member with some built-up credit. Timing is everything;) But right now is a pretty good deal none-the-less.