Anyone tried to use a waterbed mattress filled with air instead?

A Vinyl Waterbed mattress is completely different from an air mattress. When you fill a water mattress with air, it's shape becomes more blob like than mattress shaped and no it really does not hold air very well.

Air mattresses do hold air well and keep a rigid form when filled where waterbed mattresses require a frame to keep their shape. Even with that, it is not enough to chamber and baffle the air. It's like when you squeeze a balloon the air goes else where. Most air mattresses are made from vulcanized rubber where vinyl mattresses have a kind sheath of sorts to help them keep shape and hold air.

Super explanation, thanks! There goes that idea. 🙄

Air also doesn't hold body heat. It would be super cold to sleep on.

Thanks, yes that is true.

Remember when we first got a waterbed we turned off the heat when it got hot outside, learned the hard way, a horrible sleep!

ROFL. I wish I had the pics of the fun we had on a air filled mattress! Basically a waterbed mattress is a large "balloon". I decided to go with a 70% waveless so we took the old queen size waterbed mattress out to the yard and filled it with air. It was a a landing pad for run and dive onto. When the kids got tired of running & jumping we let out a little air and used it in the pool as a "raft". The kids took great delight in trying to keep upright & balance on a semi round "balloon" in the pool. It lasted a few weeks as an outdoor fun zone before it developed a hole. Then it got cut up and used to line my wood planters. I think I still have a few pieces of vinyl left from the fun 15 years ago. ( I keep finding places where the thick vinyl can be used )

If daughter is tired of the waterbed, then buy a mattress for her platform. Or, if she wants waterbed, replace side rail with a new piece of lumber from the hardware store.