The line between design patents and copyrights can be a little difficult to grasp sometimes, but the difference ultimately comes down to whether the design has a function.
A classic example of a copyright might be a photograph. The only function of a photograph is looking nice. On the other hand, a good example of a design patent might be the grill of a car.
Without knowing more about the actual function of what you're selling, and given that, I'm tempted to say that it's more of a copyright candidate. That's out of the scope of this site, but I'll be brief. Copyrights are immediately granted upon creation of the work, so you already have one! There are some significant advantages to registering your copyright early, but you can do that at any time. If you haven't already copyrighted your best-selling work, I would suggest it. It's something like $35, so it's probably worth it.
But that said, that will only protect you in the case of this very implementation. I could slightly alter the design of your product and avoid infringing on your copyright.
I'm not sure there will be a way to protect this specific product in a broader way, unfortunately. I'm disregarding the bar of public disclosure, which I imagine would be a hindrance anyway (if you publicly disclosed your product over a year ago, it's no longer patentable), but in order to get true protection in most cases, you'd want a full-on utility patent. As the name suggests, however, utility patents need to have some utility. Again, from my limited understanding of your product, I'm not sure your product would meet that requirement.
Speaking more particularly of the application (and that's an important note: this is an application, not a patent), I'd be a little surprised to see it go through. If nothing else, I'd be quite surprised to learn that there wasn't significant prior art that would make it "obvious" (quotes because it's a buzz-word with patents) to anyone in the field. It's also not a particularly well-worded patent.
If it did go through, you'd have to look at whether you were infringing, regardless of the patentability of your own implementation. Now, finally, I'm getting a bit to the title of your question, and their similarities. I imagine you're far more familiar with your own designs than I am, but the key is to read the claims. They're the important part of any patent application. The first claim to the one you're referencing reads as follows:
An accessory for covering an object, said accessory comprising:
a plurality of strands having a neck region and a skirt region, wherein said plurality of strands in said neck region are connected together so as to form an opening through which an object may be inserted, and wherein said plurality of strands in said skirt region are configured to hang loosely from said neck region and to cover said object.
From the image you've uploaded and that claim, I'm inclined to say that you wouldn't be infringing.
I've said a lot, some of it may be immediately relevant to you and some might not be, but I hope you can piece together something from all this information that will help you find the appropriate course of action. From what little I've seen, I would suggest a copyright.