Maybe you are talking about low profile Japanese platform beds.
Here are your answers:
1. Yes, fabric wrapped bed frames are hard to clean and maintain than metal or wooden frame. Fabric can hold lot more dust than plane wood or metal and you can't simply clean them, you have to spend time to clean them. Using vacuum can be a option to clean those frame.
2. It depends on your bed height, if your bed is low profile then it can be a little bit difficult for pregnant woman to use the bed. There is solution too..you can get a box spring and put it under your mattress. It will raise your bed height.
3. Go for a co sleeping crib, it's the best option according to me.
4. You can buy or make a custom platform bed. For making your own platform bed contact with carpenter near you they can help you about this. And search online for designs you will get a lot of idea. And if you want to buy one then you can get a ready made one from any furniture shop who sales platform bed or you can buy from online. My suggestion is to before buying platform bed from online store read recent customer review and opinion about the product to avoid making wrong selection.
I hope it helps, Thanks!