An attorney, per se, can't protect your idea, but an IP attorney can advise you on the options available to you, and advise you on the best way to protect your idea, given the subject matter, the likely applications of the idea, and the amount of money you're willing to invest.
A provisional patent application is an inexpensive way to get started, but it only buys you time (a year, to be exact). After the year is up, you have nothing, unless you file a regular patent application before the anniversary.
A provisional application can be a very simple sketch or outline of the invention, but a good provisional will be almost as extensive as the corresponding utility application itself (and almost as expensive to prepare, although much less expensive to file). The more information you can get into your provisional, the stronger your position will be in any patent that is eventually issued. If your provisional is sparse and vague, you may eventually face an argument that you didn't really know how to make or use the invention when you filed the provisional -- and that somebody else figured it out before you did.
Contact an IP attorney for further information. Patent law can be a bit tricky, and if you really have a great idea, it'd be a shame if you missed out on any of the opportunities it could bring to you.
In addition to the previous suggestions, yes, you should submit all of your designs and "possible variations" in your provisional patent application (PPA) to support and strengthen your eventual utility patent application, particularly its claims. It would be best to consult a patent attorney early to guide you through the patent process, which is complex. At the very least, you should consider retaining a patent attorney when it comes time to prepare the utility patent application.
Turning to another part of your questions, you mention ordering an "application for a provisional patent." Actually, there is no "application" for a PPA. The U.S. Patent and Trademark Office simply requires a written description of your invention, and drawings if necessary, a filing fee, and a cover sheet for a PPA. You can read about those requirements here: http://www.uspto.gov/patents/basics/index.html#prov
and here: http://www.uspto.gov/patents/resources/types/provapp.jsp
You can find forms, including a provisional cover sheet, here: http://www.uspto.gov/forms/index.jsp#patent
By the way, inventors should be careful of invention assistance companies. Some of these are scams and simply take your hard earned money to do what you could have done yourself. Worse still, such companies often only delay or jeopardize an inventor's patent rights.
While you do not need an attorney to protect your original idea, I have found the following analogy helpful:
You do not need an architect to build a building. However, the more valuable the building, and the more valuable the land the building is built on, the more likely you are to maximize the value of your property by using a skilled architect.
Similarly with patents, you may not need a patent attorney to get a patent issued, but in order to maximize the value of a potentially valuable invention, a skilled patent attorney can help you to capture more of the scope of your invention.
I would take some time to reflect if you have is one such invention that would benefit from a skill professional assisting you in maximizing its value.
A provisional U.S. patent application is the first step in a cascade of activity that might result in the grant of a U.S. patent and/or one or more foreign patents. To meet the legal requirements, the application must contain a disclosure of the invention in enough detail to enable someone skilled in the pertinent field to make and use the invention, and (per judge-made law) a "written description" that describes the variations that the inventor considers to be within the scope of the patentable subject matter.
Beware: if a court eventually decides that the provisional patent application didn't meet the legal requirements, then the applicant can sometimes wind up with zero patent protection, even if the Patent and Trademark Office granted a U.S. patent on a later-filed nonprovisional U.S. patent application. This is the story of the sadder but wiser New Railhead Manufacturing LLC as described in the links I am providing below.