Is it okay to write a utility model patent like this?

No, because a utility model only protects the changes in the structure and positional relationship of the product, and the formula of product materials and manufacturing process cannot be applied for as a utility model.

It depends on whether your A is an existing technology. If it is an existing technology, you can write it like this, a kind of glove. The other characteristics are that it is sewn from A fabric. If fabric A is a fabric that has not yet been disclosed, you can apply for invention.