My eyelids are always changing shape.

I would recommend posting some pictures, or getting an in person physical examination. Without pictures its difficult to get an idea what you are referring to.

If your folds are all over the place, you probably lack a hard attachment between the eyelid skin the elevator tendon.  Eyelid surgery can be used to establish this attachment.  The procedure is called an anchor blepharoplasty.

I think what you mean by changing eyelid shape is the change of the upper eyelid crease. Loosely formed eyelid crease, either natural or formed by surgery, can be influenced by the puffiness of the eyelids. The eyelid tissue is very soft and can be easily puffed up (or swollen) due to various reasons. When that happens the location and/or the shape of the upper eyelid crease can change. The solution for that problem is creating a more firm line (this does not mean it needs to be un-natural).