Take a look at the link in my signature to a real simple Layer Mask tutorial. Even though it targets GIMP, the concept remains exactly the same for PS or any other image editing software that has layers and layer masks(even if the exact steps are a tiny bit different). Using Layer Masks correctly, you can get blending results that would meet your needs and yet never have to "destroy" the contents of the layers, ie, it's easy to undo, add more, remove some, etc at a moments notice.